He has been identified as an 18-year-old Salt Lake City resident, but police have not yet released his name.
Salt Lake City police spokeswoman Robin Snyder, speaking to reporters about 4 a.m., just minutes after authorities removed the last body from the downtown mall, also declined to name any of the victims.
Snyder described them as two 28-year-old women, a 52-year-old man, a 24-year-old man and a 15-year-old girl.
The 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 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.
Police plan to release the name of the shooter sometime later today, Snyder said.