1. He doesn't sound like a sociopath. He expresses remorse, describes himself as "evil", seems shaken by the violence, and took the initiative to turn himself in. None of that is consistent with sociopathy.
2. The flat, emotionless cadence of his voice during the call suggests profound shock. As someone who has experienced profound shock first hand, that numb, almost trance-like quality of speech is extremely familiar.
I really, really feel for the father and the two remaining sisters. They essentially lost three family members to this...two dead, and the other changed irrevocably from the person they thought they knew.
I don't know what to think about Jake. Mental illness is not a get out of jail free card for destructive behavior. That he snapped with so little apparent provocation or warning makes the threat of recidivism extremely worrisome were an attempt to made to rehabilitate/release him. Thankfully the decision isn't in my hands.