Salt Lake City ? An off-duty police officer having an early Valentine’s Day dinner with his wife was credited Tuesday with helping to stop a rampage in a crowded shopping mall by an 18-year-old gunman who shot five people to death before he was killed by police.

A day after the shooting, investigators struggled to figure out why a trench-coated Sulejmen Talovic opened fire on shoppers with a supremely calm look on his face.

The teenager wanted “to kill a large number of people” Monday and probably would have killed many more if not for the off-duty officer, Police Chief Chris Burbank said.

Ken Hammond, an off-duty officer from Ogden, north of Salt Lake City, jumped up from his seat at a restaurant after hearing gunfire and cornered the gunman, exchanging fire with him until other officers arrived, Burbank said.

The victims were identified as Jeffrey Walker, 52, Vanessa Quinn, 29, Kirsten Hinkley, 15, Teresa Ellis, 29, and Brad Frantz, 24.

Four people who were wounded remained hospitalized.