Since his mathematical abilities have nothing to do with it otherwise, I suppose the author chose to make the character a mathematician because it fits a stereotype of a sociopath. In fact, in one particularly offensive line the killer says that his math degree is "useless except that it promotes schizophrenia". In my opinion, this offensive stereotype is abused in fiction and I fear that it may have negative consequences for the discipline. I have seen no evidence that schizophrenia occurs with any greater frequency among mathematicians than it does in the general population. For example, I can think of only one famous mathematician who had/has this disorder, and that is John Nash. Similarly, the only sociopathic mathematician I can think of is Ted Kaczynski. Note that these two form a very small subset of the set of all mathematicians in history, the vast majority of whom were perfectly sane. Yet, somehow it has become standard in fiction that some huge number of mathematicians are murderous schizophrenics.

This movie/play is not that bad in most ways. Some may complain that it is overly verbose, but that is because it is a thinking-person's movie and not a shoot-em-up adventure. However, I am sufficiently tired and annoyed by the "crazy killer mathematician" stereotype that I cannot bring myself to recommend that anyone watch or read it.