In exploring a hypothetical situation, I ran across this problem and I'm curious to know the answer, but math's not really my forte.
You have a pool of 15 people. Between these 15 people there will be five murders. Each murder will have one killer and one victim, with the exception of the third, which will have two victims. Note that the killer and victim can be the same person; a suicide. After each murder, both the victim and the killer are removed from the pool of possibilities. In the third murder, one of the victims can also be the killer, but the other must be different. Both victims are found in different circumstances, so order matters; Person A being Victim 1 and Person B being Victim 2 are not the same as Persona A being Victim 2 and Person B being Victim 1.
Knowing all this, what is the total possible number of combinations of killers and victims for all five murders together?
A beginning:
There are six victims in all. Five of them (victims number 1,2,4,5,6) could independently be victims of a murderer or of suicide. This gives $2^5=32$ different plots for a crime story. Now we have to take the names of the involved persons into account. A plot with $s$ suicides involves $12-s$ persons entering the scene in a certain order (in case of a murder the murderer precedes his victim). The total number of possibilities is then a sum over $s$, $0\leq s\leq 5$ of products of binomial coefficients and the like.