COLUMBIA, Md. (AP) — The 19-year-old Maryland mall gunman was a skateboarding enthusiast who took a taxi to the mall, carrying a 12-gauge shotgun he'd purchased legally a month earlier, plenty of ammunition and some crude homemade explosives inside a backpack, authorities said.

Darion Marcus Aguliar entered the Mall in Columbia around 10:15 a.m. Saturday near Zumiez, a shop that sells skateboarding gear, and went downstairs to a food court directly below. Less than an hour later, he returned to the store, dumped the backpack in a dressing room and then started shooting, police said.

Shoppers fled in a panic or barricaded themselves behind closed doors and police arrived within 2 minutes of the first 911 call. They found three people dead, including Aguilar, who killed himself, police said.

The shooting has baffled law enforcement and acquaintances of Aguilar, a quiet, skinny teenager who graduated from high school less than a year ago and had no criminal record. Police spent Sunday trying to piece together his motive, but by late afternoon, it remained elusive.

After Aguilar had fired between six and nine shots, two Zumiez employees were dead, police said. 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. Although they lived close to Maryland's largest university, neither was a student there.

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

Tydryn Scott, 19, said she was Aguilar's lab partner in science class at James Hubert Black 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 graduated in 2013, school officials confirmed.

"There are a lot of unanswered questions," Howard County Police Chief William McMahon said at a news conference. Aguilar purchased the shotgun legally last month at a store in neighboring Montgomery County.

It took hours to identify the gunman since he was carrying ammunition and a backpack containing homemade explosives, McMahon said. Officers searched Aguilar's home Saturday night, recovering more ammunition, computers and documents, police said.

The home is a two-story wood-frame house in a middle-income neighborhood called Hollywood, near the Capital Beltway. No one answered the door Sunday morning. There was a Christmas wreath on the front door and signs that read "Beware of Dog."

Aguilar and his mother rented the home. Sirkka Singleton, who owns the property with her husband and lives a block away, said they use a property manager to find tenants and have never met the Aguilars. She declined to say who the property manager was.

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.

Residents described the neighborhood as a mix of owners and renters, including some University of Maryland students. But university spokeswoman Katie Lawson said neither the victims nor the gunman attended the school.

A man who answered the phone at Johnson's residence in Mount Airy, northwest of Baltimore, said the family had no comment. The victim's aunt told a local television station that she did not believe her nephew knew Aguilar.

Sydney Petty, in a statement to WBAL-TV, said she did not believe her nephew had a relationship with Benlolo.

"Tyler didn't have anything beyond a working relationship with this girl, and he would have mentioned it if he did, and we're just as confused as anybody," Petty said.

She said her nephew also worked at a drug rehabilitation center in Mount Airy, for which she served on the board.

Five other people were hurt in the attack, but only one was hit by gunfire — a woman who was in the food court downstairs from the store and was hit in the foot. All were released from hospitals by Saturday evening.

At the time of the shooting, the mall was busy with weekend shoppers and employees.

Police searched the mall with dogs overnight. Stores were to reopen Monday afternoon.

Benlolo's grandfather, John Feins, said in a telephone interview from Florida that his granddaughter had a 2-year-old son and that the job at Zumiez was her first since giving birth to her son.

"She was all excited because she was the manager there," he said.

He described his daughter's family as a military family that had moved frequently and had been in Colorado before moving to Maryland about two years ago. He said his granddaughter was on good terms with her son's father, and they shared custody.

"I mean, what can you say?" he said. "You go to work and make a dollar and you got some idiot coming in and blowing people away."

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Associated Press writers Jessica Gresko and Martin Di Caro in Washington, Eric Tucker in Columbia, Md., and Kasey Jones in Baltimore contributed to this report.