Homicide, as the ultimate expression of violence, is the result of an interaction between internal and external phenomena. While external factors include education, living conditions, familial, cultural and peer influences ^1,2, the psychiatric condition of the killer is included among the internal factors ^3,4. Furthermore, some studies have shown consistent data on the characteristics of a typical parricide offender ^3-5. In this regard, mental illness, especially schizophrenia, has been consistently associated with the occurrence of parricides ^6,7. Although previous research has shown that severe mental illness is prevalent among adult parricide offenders ^8,9, studies conducted in forensic secure hospitals are still scarce ⁷.

Parricide is technically defined as the act of killing one's father, mother, or another close relative ³. The term originates from Latin (parus: relative and caedere: killer); parricide refers to the murder of the father and matricide to the murder of the mother ³. The killing of a parent by sons or daughters is one of the most shocking crimes, commonly receiving tremendous media attention and generating bewilderment and doubts regarding the motivations behind the killings ¹⁰.

The low prevalence rates of parricide poses a number of challenges to research, especially when mentally ill parricide offenders are involved ^11,12. In the United States, parricide accounts for approximately 2% of homicides in which victims knew the offender ^13,14; other countries show similar estimates: parricide accounted for 2-3% in a year in France ¹⁵, for around 4% of all homicides ¹⁶ and 9% of homicides occurring in a domestic context in Canada ⁵, and for 1.7% of all homicides during a nine-year period in North Portugal ¹⁷. Although it is highly infrequent ^13,14, this form of interpersonal violence has severe consequences for families and society ¹⁰.

This study provides an investigation of victims, killing methods and characteristics of parricide offenders committed to a forensic inpatient mental health facility in Brazil (the Forensic Psychiatric Hospital Doutor Maurício Cardoso). It also analyses the homogeneity of the parricide phenomenon by comparing the results obtained with those yielded by previous studies.

The sample consisted of patients with parricide as index offence under psychiatric care from January 2012 to February 2013 in the

Forensic Psychiatric Hospital Dr. Mauricio Cardoso in Rio Grande do Sul, Brazil. Data were collected from personal interviews with the patients and through their medical and legal records. This is the only forensic psychiatric hospital in the state of Rio Grande do Sul, and is the reference center for all forensic psychiatric evaluations in the criminal scenario of the southernmost state of Brazil.

Patients were sent to this forensic psychiatric hospital due to one of these two conditions ¹⁸:

Conviction of parricide, with criminal commitment as a substitution for punishment. Criminal commitment in Brazil is known as Safety Measure, and consists of the coercive application of psychiatric treatment, generally in-hospital. It is similar to the verdict "guilty but mentally ill" in English-speaking nations. Acquitment based on the incompetence of the defendant undergoing treatment in a psychiatric hospital. It is similar to the "not guilty by reason of insanity" verdict of the Common Law.

A cross-sectional analysis of the sociodemographic variables of parricide offenders and their victims, as well as of crime characteristics and psychiatric diagnosis of perpetrators was conducted. Categorical variables were expressed as absolute frequencies and percentages; continuous variables were expressed as mean and standard deviations or medians and amplitudes, depending on the distribution of data. When appropriate, chi-square analyses were done to determine whether differences were statistically significant, and the significance level was set at 0.05. A narrative review was performed using the LILACS, SciELO and PubMed database, having parricide, matricide and patricide as key words; all papers published in the last fifty years (given the rare nature of parricide) in English, Portuguese and Spanish languages were considered.

This study was approved by the Hospital's Research and Ethics Committee and all patients consented the research.

In 2012, there were eighteen patients with parricide as index offence under psychiatric care in the Forensic Psychiatric Hospital Dr. Mauricio Cardoso. All parricide offenders were males (n=18, 100%) and mostly white (n=15, 83.3%); their ages ranged between 18 and 48, with a mean age of 29.2 (SD=9.4), a mean of received education of 5.4 years (SD=3.9), predominantly single (n=17, 94.4%) and unemployed at the time of the offense (n=14, 77.8%). According to the criminal files, 77.8% (n=14) of the patients did not have any prior convictions.

In 55.6% (n=10) of the cases, only the biological father was murdered (patricide); in one case (5.6%) the non-biological father was the victim (step-patricide); 33.3% (n=6) corresponded to only the biological mother (matricide), and both biological parents were murdered in one case (double parricide). Eleven offenders (61.1%) had a psychotic motive for committing the crime, and 16.8% (n=3) committed it under the influence of drugs. Following the parricidal act, five patients (27.8%) attempted to escape from the crime scene, one (5.6%) patient attempted suicide after killing his father, and another one dismembered his mother's corpse before trying to conceal it.

38.9% (n=7) of the cases had a history of domestic violence; four patients (22.2%) were physically abused by their parents, although none had a history of incestuous behavior. Three patients (16.8%) had already been involved in violent acts against their parent(s) in the past. In the total sample, 22% (n=4) of the mothers suffered from a psychotic disorder and 33.4% (n=6) of the fathers presented with alcohol use disorder. The mean age of the victims was 63.3 years (SD=13.2) and ranged between 43 and 75. Most crimes (n=15, 83.3%) were committed inside the parent's household, and in 77.8% of the cases (n=14) the aggressor and the victim lived together, while in 44.5% of these situations the family was constituted only by the attacker and the parent(s).

The killing methods/weapons included sharp force trauma in 44.4% (n=8) of the cases caused by knives (n=4) or axes (n=4); blunt force trauma in 44.4% (n=8) caused by battering (n=5), non-firearm blunt objects (n=2) or firearms (n=1), and strangulation in 11.1% (n=2). None of the killers committed the parricide in association with another person.

Among the 18 parricide perpetrators, 83.3% (n=15) had been diagnosed with a psychiatric illness before the index offense; although 86.7% of them (n=13) had already received inpatient psychiatric treatment during their lifetimes, only 11.2% (n=2) were under psychiatric care at the time of the murder. All patients were evaluated by a forensic psychiatrist after the offence, and received the following diagnoses: schizophrenia (n=11, 61.1%), antisocial personality disorder (n=3, 16.7%), moderate intellectual developmental disorder (n=2, 11.2%), bipolar disorder (n=1, 5.6%), and severe substance related disorder (n=1, 5.6%).

All patients were hospitalized in secure units when this research was conducted; 77.8% (n=14) of them went from high to low or median security, moment when, under explicit conditions, the releasing of the patient is possible for a certain period of time (progressive release). They have undergone psychiatric treatment at the Forensic Hospital for a mean of 10.7 years (SD=8); nevertheless, in 72.2% (n=13) of the cases, there was at least one non-violent act related to disciplinary issues during their commitment in the Forensic Hospital (safety measure), mainly drug abuse or attempts to escape.

Although this topic is highly relevant, in-depth discussions on the aspects behind parricide are limited because it is relatively uncommon ^{5,11-15,17,19}. Indeed, such aspects are frequently described as part of intrafamilial homicides as a whole, instead of a single issue ^20,21. So far, available data on Brazilian parricide perpetrators is scarce ²²; in addition, only few studies have been conducted with patients in forensic psychiatric hospitals worldwide ^23,24. However it is important to note that, in many countries, parricides are sent to prisons and not to psychiatric hospitals, as in Brazil. The sample of the parricide population considered for this study is likely to be representative of parricides in Brazil, providing insightful information regarding offenders under commitment in a forensic psychiatric hospital.

The results presented here coincide with most research on parricide offenses; the typical parricide offender is a single, unemployed, poorly educated, young, male adult who lives with the victim ^{5,15,17,23,25}. As in this research, most parricide offenses involve a single victim and a single offender ²⁵. Moreover, researchers found that attempted and completed parricides are quite similar ^19,26.

General perception dictates that most parricides are committed by sons. For instance, data from the Broadmoor Forensic Psychiatric Hospital in England document a son to daughter ratio for matricide of 4.8:1, where only twelve female patients have been admitted for this crime in a 46-year period ²³. Matricides committed by juvenile females are even less frequent, raising speculations on whether they committed suicide before being sent to prison or were committed to a forensic hospital ¹⁵. As other authors state, Heide and Pette ²⁷ found that sons were significantly more likely to participate in the killings of both mothers and fathers than daughters, although higher rates of female killings were shown (16% and 13%, respectively). Interestingly, Baxter et al. ²⁸, who analyzed almost equal numbers of matricides and patricides, found that those who committed matricide were not distinguishable from those who committed patricide in terms of sociodemographic and psychiatric variables, suggesting that the act of killing a parent was more important than whether the parent was the mother or the father (28). Notwithstanding, mothers have a higher risk of becoming victims of homicide by patients with schizophrenia, as noted by some studies ^7,15, including this.

In most parricide cases, as in those observed in this research, the murder takes place at the victim's household -most parricide perpetrators live in the same household as their victims ²⁸- whereas killings committed by strangers usually occur in public places ²⁸. Likewise, concealing the corpse or attempting to escape after the killing are less usual ^9,28 and, as demonstrated here, parricide offenders tend to act alone ¹². Furthermore, as stated by Baxter et al. ²⁸, those who kill strangers usually have a longer criminal history as compared with those who commit parricide.

According to some authors ²⁹, adolescents are more likely to use firearms to kill their parents because they are usually physically weaker than the later. In addition, spontaneous gun usage outnumbers premeditated gun usage in these scenarios, where, typically, the death of the parent is the result of a rapid escalation of the situational forces at stake ²⁰. Moreover, patricide victims are more likely to be killed withguns than matricide victims ^20,29 -our sample has almost twice as many fathers than mothers. In contrast, adult parricide perpetrators kill more frequently while they are close to their victim; in the sample considered for this study, only one patient used a firearm for the killing, possibly showing that only parricides committed by adults were evaluated.

Although it is possible to speculate that parricides could be reduced if access to firearms were restricted ²⁹, this hypothesis cannot be supported by the data presented here. Importantly, painful killing methods and/or excessive violence are frequently seen in these murderous acts ³⁰, sometimes leading to the dismemberment of the victim's body ^22,31. The high prevalence of elderly population among victims, as well as the small number of inhabitants in the household -where the crime was executed- highlight the vulnerability of the victims ^30,32.

One of the first explanations for the parricidal act was predominantly psychodynamic, related to the Oedipus complex, suggesting that killing a parent represents a defense against hostile or incestuous impulses. Accordingly, a son who commits matricide is typically young and single, with an absent or passive father figure and a mutually dependent and hostile relationship with his mother, marked by the son's difficulty for breaking away from the mother's dominance ^33,34. Meanwhile, the father-son relationship in patricide is typically punitive ⁴; in this sense, perpetrators usually feel relief rather than remorse following the patricidal act ⁴.

As described here, high rates of mental illness are typical among parricides, particularly schizophrenia, personality disorders (especially antisocial), and substance related disorder (especially alcohol) ^{5,9,10,13,20,28}. Noteworthy, most of the patients in this study presented with delusions regarding the victim and killed them in a brutal manner ⁹. In this vein, undetected or untreated severe mental illness is an important contributing factor to parricide ^11,35. Interestingly, previous violent acts towards parents are also a risk factor for parricide, although they are not found in the majority of parricides, as demonstrated by Singhal and Dutta ⁴ and corroborated here.

Among schizophrenics, matricide occurs more often than patricide. Hence, victims and offenders living together, a provoking event before the homicide, and the female sex of the victim are significantly associated with parricide by a schizophrenic son ^34,35. Matricides have also been related to Capgras delusion (the attacker believes that his parent has been replaced by an impostor), threats of involuntary hospitalization, and compulsory pharmacotherapy ⁷. In a study conducted by Liettu et al. ³⁶ one third of the males who commited parricide died by suicide. Additionaly, Devaux et al. ¹⁵ reported a rate of 17% of suicide attempts after killing a parent, highlighting that the dynamics of parricide-suicide is more frequent among schizophrenic offenders.

According to Hillbrand & Cipriano ²⁶, most parricides fall into one of two categories: adolescents without a conduct or psychotic disorder, or untreated psychotic adults who usually suffer from schizophrenia with comorbidity of alcohol or drug abuse; the number of matricides in adolescent samples is substantially smaller than the number of patricides ³⁷. The main reasons for killing are usually delusions or financial conflicts in adult samples, and attempts to escape from an abusive father in juvenile samples ^32,37. Furthermore, offenders who kill stepmothers tend to be younger than those who kill biological mothers ^13,37. Another rare but shocking scenario corresponds to matricide committed by male adolescents who were in incestuous relationships ³⁸, like the murder described by Schlesinger ³⁸, followed by vaginal and anal necrophilia.

So far as known, this is the first study conducted with the parricide population of a Brazilian forensic psychiatric hospital. In the light of the challenges that parricide studies impose, this research provides evidence of important factors, therefore, contributing to knowledge on this uncommon offense. Notwithstanding, the results exposed here are limited due to the relatively small sample considered and the cross-sectional nature of the study ²⁶.

A forensic psychiatric evaluation of parricide offenders should be warranted given the high prevalence of mental illness among these perpetrators. Although schizophrenia was the most common diagnosis at the time of the index offence, it is not the sole cause of parricide. Finally, the pattern observed in this study, regarding weapon usage, shows that the characteristics of victims and offenders coincide with previous research, allowing to conclude that the phenomenon of parricide is relatively stable and homogeneous.

Conflict of interests

None stated by the authors.

Funding

None stated by the authors.