The man didn't speak but was carrying a gym bag with a note inside it. He was found dead in the gym lying on top of one of his guns near a victim, said Charles Moffatt, Allegheny County police superintendent.

At least 10 other people were injured in the barrage of bullets that sent people in the gym ducking for cover, Moffatt said.

A law enforcement source identified the gunman as George Sodini, a 48-year-old gym member.

Moffatt would not release the name of the victims during a Wednesday news conference.

The gunman apparently was on a mission, Moffatt said.

"He did what he set out to do, and I think nobody could have stopped him, " he said.

Moffatt would not confirm a newspaper report that Sodini's ex-girlfriend was one of the women killed in the shooting.

He also did not say what was written on the note that was found in Sodini's gym bag.

Sodini entered the fitness center around 8 p.m. Tuesday and went straight to an aerobics classroom, where he opened fire with multiple handguns, Moffatt said.

The shooting victims arrived at three major hospitals in the area.

A spokeswoman for UPMC Mercy Hospital confirmed five female shooting victims arrived at the facility with multiple gunshot wounds. "All arrived in critical condition," hospital spokeswoman Linda Ross said. "Three of them were upgraded to serious condition overnight."

Allegheny General Hospital received two wounded patients at its trauma center, a spokesman said. Both victims are women and were listed in fair condition early Wednesday.

A St. Clair Hospital spokesman said three shooting victims arrived there Tuesday night; two were in stable condition and one, who was shot in the chest, died at about 8:55 p.m.

Perry Calabro of nearby Bridgeville told CNN he was between racquetball games at the gym when he suddenly heard screaming and multiple gunshots. He said he ran out but didn't see the gunman or others.

Other witnesses told CNN affiliate WTAE-TV in Pittsburgh that the lights went out before they saw flashes in dark, later realizing it was gunfire.