The murders of director Rob Reiner and his wife, Michele Singer Reiner, have rocked Hollywood, especially after their son Nick was arrested in connection with their brutal deaths. Us Weekly exclusively spoke to two experts in the area of parricide - the act of killing one's parent or relative - who discussed what might drive a child to murder their loved ones, as well as the signs and preventative measures to avoid such a tragedy. Denise Paquette Boots, a criminologist in the Public Policy Program at University of Texas at Dallas, and Dr. Kathleen M. Heide, a distinguished professor at the University of South Florida and author of Why Kids Kill Parents, who have not studied Nick's case, told Us that parricide offenders are broken down into a "four-part typology": the severely abused adolescents, the mentally ill, the antisocial and the enraged offender. "Severely abused kids who kill parents [are] individuals who kill parents because of longstanding abuse, which can be documented," Heide told Us. Rob Reiner's Son Nick Was 'Always Hostile' Toward Family Before Murders "Severely mentally ill parricide offenders are individuals who by definition have a severe mental illness, typically psychosis, so along the schizophrenia spectrum, and then sometimes bipolar disorder or major depression with psychotic features. "Dangerously antisocial [offenders] kill because the parent is an obstacle or they kill for a selfish instrumental reason. It could be to get money, it could be to get freedom, it could be to date the person they want to date," she explained. "[The] fourth type is enraged, and these are individuals who very often, not always, but have a substance abuse disorder. And the important part is they have a lot of underlying anger, which may be related to abuse or may not, but the point is that they kill their parents when they are enraged," Heide continued. "And often in these cases, their parents have been overindulgent. And then finally, say to their son or daughter, it's time to grow up and do a little bit of tough love or setting what we'd say are appropriate boundaries. And these individuals who could be adolescents or adults have very little frustration tolerance and kill out of rage." Nick, 32, had openly struggled with substance abuse, and insiders previously told Us that he had "always been hostile and volatile" toward his family. Rob Reiner and Nick Reiner Laura Cavanaugh/FilmMagic "Healthy, happy kids, of whatever age, don't kill their parents," Heide said. "Why does this crime evoke horror? It's so taboo because the one thing you don't do is kill the very people who gave you life." She added: "The reasons can be many. But the point is there's always a reason." While parricide is the "rarest of the rare," making up only one to two percent of homicides (according to Heide, about 20 cases at most a year among juveniles and adults), Boots told Us the majority of adult parricide perpetrators are the mentally ill, and the crimes are "typically committed with firearms." "The second highest is actually with cutting instruments," she said. (Rob, 78, and Michele, 68, were stabbed to death.) Heide also weighed in, sharing that stabbing is always "a more personal type of killing. It also involves more effort." Rob and Michele Reiner's Son Nick Reiner Arrested After Parents' Murders "When the victim is known, it can indicate more of [an] emotional connection and can also tell you something relationally what's going on there," she said. "So it's certainly significant." Boots outlined the typical parricide profile, telling Us that offenders often have "less of a history of offending and delinquency than other types of homicide offenders, and they're typically white [males], unmarried and unemployed. They commonly live with their parents at the time of the offense." (Rob and Michele's son lived with them in their Brentwood, California, mansion). According to the professor, parricide offenders are usually in their early 20s or early 30s. "It's more common that only one person is killed. But it's not uncommon that we see two victims, and it's both parents," Boots said, pointing to a study she did with Heide, in which they discovered that out of 147 homicides, "about 59 percent of the parricides were one victim, and 27 percent were two victims." Rob Reiner's Son Nick Praised His Parents in Past Interview: 'I'm Lucky' She shared that "63 percent involved a father being killed, and 61 percent a mother was killed." Boots added, "What we see in some of the severely mentally ill parricide offender typology is that mothers tend to be caretakers. Normally, it's not uncommon that a mother is killed in those instances, but fathers are also killed. It's a double tragedy." According to Boots, "This is a gendered crime. It is a male-dominated phenomenon. It's not that girls don't kill their parents, but it is a much rarer parricide. Offenders are usually male." Parricide crimes are not discriminatory, as seen in the case of the