I would not go with bluetooth enabled chip in his head that directed his planning and actions but someone somewhere must have known or aided in the planning and execution.
He could have been working with anyone from ISIS, BLM, the SLA, KKK, Antifa, Black Panthers, an American militia, FSLN, Sendero Luminoso, CPP, NPA, FARC or FALN.
He was a Sleeper Cell and while it could be that he was a one man Sleeper Cell, he might have been part of a much larger domestic, foreign of hybrid terrorist organization.
All anyone needs to know is “Dead men tell no tales.”