A caretaker at a group home for the mentally ill called police in the middle of the night because a one-armed, one-legged man in a wheelchair was angry and wouldn't calm down.

What happened next is the subject of an investigation that now involves the FBI. One of the two Houston police officers who entered the home fatally shot the double-amputee in the head, saying he was cornered by the wheelchair and thought his partner was being threatened by what turned out to be a ballpoint pen.

Houston's police chief responded Monday to escalating criticism about the weekend shooting by cautioning against a rush to judgment. Community and civil rights groups say the incident is another example of problems the police department has with using excessive force.