No public statements that I've been able to find have identified witnesses or method.

I don't know if the relevant news reports had been released at the time this comment had been posted, but the apparent method of Swartz's death was hanging.

When you narrow down the set of people who could be considered Aaron Swartz's enemies to those who could have him killed and have it reported as a suicide, who would benefit more from his apparent death by suicide than his being drained of funds and convicted of felony, and ask whether this is realistic behavior for the remaining members of that set, particularly when you consider that the individual in question had written about his struggles with depression and was facing the prospect of dramatically worsening life conditions, I think this sort of speculation is more naive than cynical.