The homicidal triad and the Macdonald triad are essentially the same. They both highlight three major personality traits in children that are said to be warning signs for the tendency to become a serial killer. They were first described by J. M. Macdonald in his article "The Threat to Kill" in the American Journal of Psychiatry.

Beginning from childhood, there are three main signs that denote a killer. Those signs are known as the homicidal triad usually referred to by Criminologists. They are firestarting, bedwetting (after age 15), and cruelty to animals and other children (Douglas and Olshaker, 2000). Firestarting is when a child or adult sets fires simply to watch something burn (pyromania). Pyromania can also be labeled as pyrophillia, because pyromaniacs receive sexual satisfaction from setting and watching fires. Bedwetting after age 15 is another sign of homicidal tendencies. It's common that burglars will urinate or defecate in houses which they are burglarizing. Killers have been known to urinate or defecate on bodies. This can be accompanied by urophillia (sexual arousal through urine) and urination or defecation in inappropriate places. Cruelty to animals or other children is a sure sign of homicidal tendencies. These behaviors are a warning for possible future actions. Often, animal cruelty reflects future homicidal behavior, the way they kill and torture animals will reflect how they eventually kill and torture people.

Recently this Triad, developed in 1963, has been called into question by other researchers. They note that many children and teenagers set fires or harm animals for many reasons (boredom, imitation of adult punishment of household pets, exploration of a "tough guy" identity, or even feelings of frustration). It is thus difficult to know whether these variables are in fact relevant to serial murder etiology and, if so, how precisely they matter (Macdonald, 1963).

One of the homicidal triad signs is discussed in "Cruelty to Animals and Violence to People". Existing research mentions that there are links between animal and human violence. Children who are cruel to animals are at a higher risk of committing domestic violence, child abuse and elder abuse (Petersen & Farrington, 2007). The importance of cruelty to animals compared with other childhood risk factors for adult violence is unclear. Case histories of mass murders and serial killers suggest that many of them were cruel to animals in their childhoods. Studies imply that children who are cruel to animals disproportionally tend to be violent to people later in life (Petersen & Farrington, 2007).

All three of the signs in the homicidal triad are mentioned in "What Makes Serial Killers Tick"? These secret compulsions are seen as the seeds to greater mayhem. "Violent acts are reinforced, since the murderers either are able to express rage without experiencing negative consequences or are impervious to any prohibitions against these actions (Scott, 2008). Second, impulsive and erratic behavior discourages friendships," increasing isolation." "Furthermore, there is no challenge to the offenders' beliefs that they are entitled to act the way they do." (Ressler, et al, Sexual Homicide) "All learning, according to Ressler, has a "feedback system." Torturing animals and setting fires will eventually escalate to crimes against fellow human beings, if the pattern is not somehow broken (Scott, 2008).

Formative years may play a role in the molding of a serial killer, but they cannot be the sole reason in every case (Scott, 2008). Many killers put the blame on their families for their behavior, seeking sympathy. In true psychopathic fashion, serial killers are blaming someone else for their actions other then themselves who are really to blame. If their bad childhood is the primary reason for their homicidal tendencies, then why don't their siblings also become serial killers if in fact they do have siblings (Scott, 2008)? We must look at other components to see what controls a serial killer to murder or harm other people.