My random thought on the killings (and without reading any of the posts since then):

We are *probably* dealing with someone who has played at least 1 game (Probably Capo) and saw what some of those players were capable of. They killed them off for that reason.

However, we are also not likely to be dealing with a veteran mafia player, because the killings were too high-profile and are likely to attract attention onto themselves.

So who fits this description?