The calculated, cold-blooded manner in which he took this woman's life demonstrates a visceral brutality that is indicative of someone who has killed before.
These aliens have a distorted sense of self-preservation that allows nothing to stand in the way of their own survival.
Guy was probably sucking up numerous US govt benefits, as well.
Authorities ought to check on how many SS no's, visas and identities he has, and the number of UI, Workman's Comp, and welfare programs he was enrolled in.
Not only should we ask why he is here, but why is he even alive?