Pima County Sheriff Clarence Dupnik said Saturday evening that the man linked to the shooting of Rep. Gabrielle Giffords and others might have an accomplice.

“We are not convinced he acted alone,” Dupnik said at a news conference.

Dupnik said investigators have reason to believe the 22-year-old suspect whom he would not name came to the scene with someone else. “We have photos,” Dupnik said of the gunman’s companion.

The “person of interest” is a male in his 50s. He said authorities were in an active search for the individual late Saturday.

Nate T. Gray, of the FBI, referred to bringing “those responsible” to justice.

Six people have now died in the attack, said Gray, who is in charge of the FBI office in Phoenix. Five people died at the scene and a 9-year-old girl died at a hospital, said Dupnik.

This is a sad day for Tucson ... a sad day for America,” Dupnik said.

There was no security at the event, a meet-and-greet outside a Safeway on the northwest side, Gray said. In all, 19 people were shot or injured, Dupnik said.

The names of those killed were not going to be released officially until all family members of the victims have been notified, the sheriff said.

Two of the people who were wounded have not been identified by authorities, he said.

The surgeon is “cautiously optimistic” that Giffords “may survive,” Dupnik said.

Federal Judge John Roll went to Mass, as he did every Saturday, and on his way home decided to stop and say ‘hi’ to Giffords, his friend, Dupnik said.

“He was at the wrong place at the wrong time,” Dupnik said. He called Roll a brilliant judge and a fine person.

Dupnik called two people who tackled the gunman “were brave individuals, noting that the semi-automatic pistol still had ammunition when the gunman was taken into sheriff’s custody.

He said the gunman was a subject of, “some police interest in the recent past,” and he has made death threats in the past, but not toward Giffords. There was no reason to worry about the Giffords event in advance, he said. The attack started at 10:10 a.m. amid a crowd of about two dozen people.

The gunman might have planned to shoot himself, Dupnik told reporters.