MILWAUKEE -- The FBI says the motive behind the shootings at a Sikh temple that left six worshippers dead remains unknown but authorities still haven't identified anyone other than the gunman as being responsible.

FBI Special Agent in Charge Teresa Carlson also told a Wednesday news conference that investigators determined gunman Wade Michael Page died of a self-inflicted gunshot wound to the head after he was shot by police. Authorities previously said an officer had fired the fatal shot.

Carlson says federal officials had not opened any investigation into Page before Sunday's shooting. She says investigators are interviewing dozens of people who have known Page as they work to determine for a possible motive.

Meanwhile, three people injured in the shooting remain hospitalized in critical condition. They include Police Lt. Brian Murphy. He was one of the first responding officers and was shot 8 or 9 times as he was tending to a shooting victim outside the temple.