He has been identified as an 18-year-old Salt Lake City resident. Police say they will release his name, along with those of his victims, at a noon news conference.
Salt Lake City police spokeswoman Robin Snyder described the victims as two 28-year-old women, a 52-year-old man, a 24-year-old man and a 15-year-old girl.
Their bodies were found "in various parts of the mall," Snyder said. Witnesses told The Tribune that three bodies were in Cabin Fever card store, one in Pottery Barn Kids and another outside of Bath and Body Works.
The gunman, who was carrying a shotgun, a handgun and numerous rounds of ammunition, was shot dead by at least three Salt Lake City police officers and an off-duty Ogden City police officer, who "encountered" the suspect in the mall, Snyder said.
The officers arrived within three minutes of a 6:44 p.m. call to 911 of "an active shooter," Snyder said. It is unclear if the Ogden officer was part of the "emergency action team" formed at the scene by the Salt Lake City officers. Officers are trained to form such a team during a shooting like this one, Snyder said.
"They went inside, neutralized the threat and took care of it," Snyder said.
Snyder would not say if the 18-year-old gunman, described by witnesses as a tall young man in a white shirt and trenchcoat, fired at police. No officers were injured during the incident.
Between 100 and 200 people were shopping and dining at Trolley Square when the gunman began his rampage. At least four other people were wounded and taken to local hospitals.
A 53-year-old man and a 44 year-old woman remained in critical condition Tuesday morning, Snyder said. A 34-year-old man and another man, whose age was unknown, were listed in serious condition.
Dozens of people witnessed the carnage and are being encouraged by authorities to seek trauma counseling.
A car believed to be that of the shooter's was found in one of the mall's parking lots, Snyder said. It was searched and removed from the scene, she said.
Rumors of a second shooter spread initially but within less than an hour, police determined there was just one gunman. Witnesses may have initially thought the off-duty officer, who with gun drawn was in pursuit of the killer, was also a gunman, Snyder said.
The mass killing was one of the worst in Salt Lake City's history.
"I don't know that we've had [a shooting] that's ever compared to this," Snyder said.
The owners of Trolley Square said in a statement Tuesday the mall will be closed today.
"We are devastated and shocked by this senseless, random act of violence at Trolley Square and will do everything we can to support the Salt Lake City Police in their investigation," said the statement. "Our greatest concern and prayers are with the victims, their families and loved ones."
At 8 a.m., police were doing their final walk-through of the mall, said Snyder. Members of the public can pick up their parked cars from the mall beginning at 9 a.m., but will be required to sign in with mall management outside the building first.
The 239,000-square-foot mall, built from the city's old trolley barns, was busy with shoppers and diners when the teen opened fire just after sunset. In a moment, the night turned terrible.
Lindsay Sharifi and her mother, sister and two young nieces were shopping in the Basket Loft when a couple ran in, shouting that a man was shooting near the west entrance.
The store owner locked the door and turned off the lights. Everyone huddled in a storage room. Eight in all, they stood and prayed for about 90 minutes. They heard gunshots coming ever nearer, and they heard screams.
"We were all being quiet, trying to figure out, 'Where is he?' " said Sharifi, 26. "We didn't know if he was going to come in and kill us all."
Eventually, a police SWAT team ordered everyone out with their hands up, and Sharifi and the others saw three bodies and glass everywhere in the card shop next store.
Over the hours, hundreds of terrified shoppers and diners fled the mall. Some stood expressionless, some wept, and many held children or loved ones. Others just drove home.
Countless squad cars, ambulances and fire trucks encircled the square, illuminating the night with flashing lights. Uniformed police and SWAT team members clutching rifles came and went through the parking lot and in and out of Trolley Square, searching the interior and hustling survivors outside.
Witnesses said the shooter fired randomly and calmly reloaded at least once.
Nearly two hours after the first shots, Snyder declared that the gunman was "no longer a threat." His motive was not known, she said.
Ron Mason and DeEta Barta, of Salt Lake City, said they were eating at the Desert Edge Brew Pub when they saw an armed man coming in from the west parking lot. They yelled, "There's a man with a gun," and seconds later heard about 12 shots.
Mason and Barta, both registered nurses, went to assist a younger male who had suffered superficial wounds to the right temple and ear. Though he clearly was in shock, the couple said, he told them that he saw his father go down. That man's fate was unknown late Monday.
Brad Merrill, who was outside the Old Spaghetti Factory restaurant on the mall's mezzanine, said he heard a loud noise and the sound of breaking glass.
"All of a sudden, someone barged into the mall with a big shotgun . . . he was holding it in one hand, barrel up," he said.
Merrill grabbed his young son and ran outside, calling 911 on his cell phone. His wife and three other children were hiding in a storage room inside the Sharper Image store. They got out about 7:50 p.m.
Marie Smith, an employee at Bath and Body Works, said she saw a gunman running in front of her store. She said she ducked behind the counter and saw him shoot a woman in her mid-20s.
"She screamed as she was coming around the corner, and he shot her," Smith said. "I didn't hear him say anything to her at all."
By 7:30 p.m., firefighters started handing out blankets to those assembled outside. About 100 people on 500 south waited to get to their cars in the parking lot, which was blocked by officers. Some were waiting for families to be brought out of the mall.
"Our No. 1 priority is get everyone out of there safely," Snyder said shortly after 10 p.m. She said police would keep the block secure through the night to continue their investigation.
"We're trying to figure out where this started, why it happened and how many victims we do actually have," Snyder said.
Said Salt Lake City Mayor Rocky Anderson: "An entire community is, of course, traumatized when there are such senseless acts of violence. My heart goes out to the victims, their loved ones and those who were in the area and obviously so terrified. . . . I don't know what could have motivated anybody to do this."
As midnight approached, witnesses still waited to be questioned by investigators at the Green Street private club and the Hard Rock Cafe at the square.
Utah Transit Authority buses were parked outside the square to let people come in from the cold, and yellow police tape surrounded the block. * PEG MCENTEE wrote this story. Contributing were NATE CARLISLE, RUSS RIZZO, MATTHEW D. LAPLANTE, LISA ROSETTA, MICHAEL N. WESTLEY, HEATHER MAY, STEVE GEHRKE, PETER LOZANICH, JASON BERGREEN, LISA CARRICABURU, BRENT ISRAELSEN and JESSICA RAVITZ.