CLACKAMAS, Ore. — Law enforcement officials expressed a kind of bleak gratitude Wednesday that a masked 22-year-old gunman armed with a semiautomatic rifle and extra magazines of ammunition did not do more damage in an attack Tuesday afternoon in suburban Portland.

And a close friend of the gunman expressed shock and bewilderment that someone she remembered as so mild-mannered in many ways — never even raising his voice or getting angry through 10 years of friendship — could have suddenly turned into a killer.

Two people were killed by gunman Jacob Tyler Roberts, who later committed suicide as police swarmed into the Clackamas Town Center mall. But with as many as 10,000 people crowding the mall for the holiday shopping season, the toll could have easily been far higher, authorities said.

The AR-15 rifle that Roberts carried — stolen Tuesday from someone he knew — apparently jammed at one point, said Clackamas County Sheriff Craig Roberts; shoppers and store owners locked down and took shelter; and the police arrived quickly, with as many as 100 officers on site within minutes.

“Less time to harm others,” Craig Roberts said in describing the attack’s critical moments of happenstance and training.

The victims were identified as Steve Forsyth, 45, a youth sports coach who owned a business in the mall, and Cindy Ann Yuille, 54, who was shopping. A third person, Kristina Shevchenko, is hospitalized in serious condition with at least one bullet wound, the authorities said. The police described her as a juvenile but did not release her age.

The sheriff said the gunman had no known connection to his victims.

“We don’t understand the motive for this attack,” Roberts said.

Some of the details that emerged Wednesday — a crowded food court; a hurried walk inside, assault rifle in hand; screams and chaos in panicked search for shelter — were particular to the case but numbingly similar to other recent mass shooting incidents, notably the killings in a packed movie theater in Aurora, Colo., in July. In that rampage, the accused gunman’s AR-15 also jammed, law enforcement authorities believe, limiting the number who might have been killed.

Based on witness interviews and mall surveillance tapes, authorities said Jacob Roberts arrived at the shopping center Tuesday just before 3:30 p.m., wearing what they described as a hockey-style mask and outfitted with a load-bearing vest, which allowed him to carry more ammunition.

He parked his 1996 Volkswagen Jetta in a spot near an entrance to the food court. After firing as many as 60 rounds — despite the gun jam — he retreated to a corridor in the mall and turned the weapon on himself. Only one gun was recovered, Craig Roberts said.

The mall was closed Wednesday — the possessions of shoppers left behind in panic, locked away for retrieval as the police searched for evidence. A mall manager said the shopping center’s website would be updated as to when people could return for their items.

Searches were conducted of Roberts’ Portland home and his car.

Details also emerged Wednesday about Roberts from acquaintances and neighbors.

“Jake was never the violent type,” his ex-girlfriend, Hannah Patricia Sansburn, told ABC News. “His main goal was to make you laugh, smile, make you feel comfortable. You can’t reconcile the differences. I hate him for what he did, but I can’t hate the person I knew because it was nothing like the person who would go into a mall and go on a rampage.”

Sansburn said Roberts recently quit his job at a gyro shop in Portland and sold all of his belongings, telling her that he was moving to Hawaii. He was supposed to take a flight Saturday but told her he got drunk and missed it, she said.

Jaime Eheler, a friend who lived with Roberts, said she has no answers. “I saw him yesterday, two or three hours before the shooting,” said Eheler, 26. “Something was off. There was a strange look in his eyes. ... It was not him.”

The Associated Press contributed.