COLUMBIA, Md. >> A Maryland mall reopened Monday with increased security, somber memorials and still unanswered questions about why a gunman killed two people and himself inside a store.

Crowds of shoppers were sparse in the early minutes of business, though white flowers were already scattered in a memorial fountain. As the community tried to get back to some sort of normalcy, investigators worked to piece together a motive for the shooting.

Police found a journal belonging to Darion Marcus Aguilar, 19, but they would only say that it "expressed general unhappiness." The contents, however, were enough for an officer looking into the disappearance of Aguilar on the day of the shooting to worry about the teen’s safety.

Aguilar was supposed to work at Dunkin’ Donuts on Saturday morning, but he never showed up. Police said Aguilar took a taxi to the Mall in Columbia in suburban Baltimore and entered the building near Zumiez, a shop that sells skateboarding gear. He went downstairs to a food court directly below the store, then returned less than an hour later, dumped the backpack in a dressing room and started shooting.

Shoppers fled in a panic or barricaded themselves behind closed doors. When police arrived, they found three people dead — two store employees and Aguilar.

The shooting baffled investigators and acquaintances of Aguilar, a quiet, skinny teenager who graduated from high school last spring and had no previous run-ins with law enforcement.

Aguilar, who had concealed the shotgun in a bag, fired six to nine times. One victim, Brianna Benlolo, a 21-year-old single mother, lived half a mile away from Aguilar in the same College Park neighborhood, but police said they were still trying to determine what, if any, relationship they had.

The other employee, Tyler Johnson, did not know Aguilar and did not socialize with Benlolo outside of work, a relative said.

Howard County Police Chief William McMahon said there has been speculation about a romantic relationship between the gunman and Benlolo, but investigators have not been able to establish that.

He said Monday that if the shooting were "domestic-related" he thought investigators would know more about that by this point. But he also did not rule that out.

The chief also said there was no evidence so far that Aguilar ever applied for a job at Zumiez or worked there.

On Monday, the store was covered by white boards as if it was under construction. Messages written on the boards thanked first responders and let customers know the store was closed.

Mall visitors could sign memory books and float white flowers in the mall’s fountain in memory of Benlolo and Johnson. Outside, a banner read: "Forever in our hearts."

Howard County Executive Ken Ulman was there for the reopening and said he will eat lunch with his wife and shop. He invited other people to join him.

"Send a message with your presence that you are standing with us," he said. "Let’s get back to business."

Aguilar was accepted last February to Montgomery College, a community college in the Washington suburbs, but school spokesman Marcus Rosano said he never registered or attended.

Tydryn Scott, 19, said she was Aguilar’s lab partner in science class at James Hubert Blake High School and said he hung out with other skaters. She said she was stung by the news.

"It was really hurtful, like, wow — someone that I know, someone that I’ve been in the presence of more than short amounts of time. I’ve seen this guy in action before. Never upset, never sad, just quiet, just chill," Scott told The Associated Press. "If any other emotion, he was happy, laughing."

Aguilar worked at the Dunkin’ Donuts on Friday and was supposed to open the store Saturday morning. When he didn’t show, his mother filed a missing persons report with the Prince George’s County Police Department at about 1:40 p.m., more than two hours after the mall shooting. Officers went to Aguilar’s home to speak with his mother about 5 p.m. and saw Aguilar’s journal. The portion the officer read made him concerned for Aguilar, the department said.

Police began tracking Aguilar’s phone and soon discovered it was at the mall.

At his home where he lived with his mother, officers also recovered more ammunition, computers and documents, police said. No one answered the door there Sunday. A half-mile away, a roommate who answered the door at Benlolo’s home confirmed that she lived there but declined to comment further. Two police officers went into the home after he spoke briefly to a couple of reporters.

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Tucker reported from Washington. Associated Press writer Sarah Brumfield in Washington contributed to this report.