Darion Marcus Aguilar liked cooking shows. He wanted to be a chef. He liked to spend summer afternoons at the Martin Luther King Jr. Swim Center in Silver Spring.

Harmless. That’s what his friends say. Unremarkable.

He has no criminal record that police or online court records can turn up. He’s had no contact with Maryland’s mental health system that authorities have found, law enforcement officials said.

But on Saturday, Aguilar, 19, who graduated from James Hubert Blake High School in Silver Spring in June, shot and killed two people and himself at a skateboarding and surfing clothing store at the Mall in Columbia.

Aguilar’s friends are trying to figure out what they missed or whether they should have seen the violence coming.

The Howard County Police Department has released this undated photo of Darion Marcus Aguilar, 19, of College Park, Md. (Handout/REUTERS)

“He was a good person. He always believe[d] in inner peace, that is why it was so shocking to believe that he was the shooter,” said Peter Chu, a Blake classmate who is now a freshman at the University of Maryland Baltimore County.

“He was a good kid,” Chu wrote in a series of Facebook messages with The Washington Post. “He never caused any trouble, that’s why this news is so shocking to me. He was just a really funny guy. . . . I really want to talk to him and ask him why, but he’s gone now. I want to ask him what was his motives.”

Police also are trying to figure out why Aguilar walked into the Zumiez store, pulled a shotgun and killed two employees: Brianna Benlolo, 21, and Tyler Johnson, 25. He then killed himself in the store, never going back out into the mall or threatening anyone else, even though he was laden with ammunition. Authorities said they have found no connection between Aguilar and the people he shot.

Howard County Police Chief William J. McMahon said at a news conference Sunday night that authorities had discovered a journal in a search of the College Park home Aguilar shared with his mother. McMahon said the teenager had written about his “general unhappiness” in life.

Aguilar’s parents, who do not appear to live together, declined to comment by hanging up or did not return calls. No one was at his house.

In an e-mail exchange Sunday, Jeffrey Vargas, a high school friend of Aguilar’s, said Aguilar held a variety of interests — from art to science fiction to the Grateful Dead.

“Darion was really into plant biology,” Vargas wrote. “We would talk about characteristics of different plant species while I cleaned the art room.”

Aguilar was shy and curious. He read books that offered answers on the truth of life. He did not think college was necessary, referring to it as “training wheels” for life. “What he wanted to do was travel the world and be educated by it,” Vargas said.

In contrast to the indication that Aguilar was generally unhappy, Vargas wrote that Aguilar seemed content most of the time, though he did go through issues, like many teenagers. But even when he was at his worst, “he’d still be collected,” Vargas said.

Vargas was at a loss to explain what happened and regrets not seeing Aguilar recently. “I wish I could have done something,” he said.

Neighbors in Aguilar’s College Park community said they knew little to nothing about him or his living circumstances. On Sunday, after authorities released his name, reporters swarmed to his family’s white two-story home with green shutters, where a Christmas wreath still hangs on the front door and the welcome mat reads “Bless this Home.”

Police searched the home Saturday, and one official said they took the journal, computers and ammunition, among other items. McMahon said investigators are still going through the journal and computer files.

Aguilar had attended schools in Anne Arundel County before going to Blake. After high school, he was admitted to Montgomery College but did not attend.

He worked at the Dunkin’ Donuts near Route 1 and Cherry Hill Road, near his house in College Park. He was supposed to open the store Saturday morning, two law enforcement officials said, but he never showed up. Two hours after the shooting, about 1:45 or 2 p.m., his mother reported him missing to Prince George’s County police. The mother did not seem to have any intimation of what her son was involved in, the officials said.

A Prince George’s County police investigator who had read Aguilar’s journal as part of the missing-persons inquiry — before he knew Aguilar was the mall shooter — said in a report that what he read had made him concerned for Aguilar’s safety.

Aguilar’s role in Saturday’s shooting has mystified many from his Blake social circle. On Facebook, Chu posted: “R.i.p.Darion. I couldn’t believe it when I heard the gunman was you at Columbia. Just half a year ago we were still chilling in high school laughing about our future. But it really didn’t have to end like this. . .

Several friends chimed in.

“WAIT Darion from Blake?” wrote one friend.

“Yeah it’s Darion. No one can believe this,” Chu wrote.

Fellow student Noah Sturdivant said that “when I knew him at Blake, he was a sweet person and never had an issue with anyone.”

“He was always smiling, and I never heard him raise his voice,” Sturdivant said.

But the news did not entirely shock another Blake classmate, Aaron Gayadeen.

“He was always a little bit crazy,” Gayadeen said through Facebook messages. “To be honest I am a little in shock that it was him but I’m not too surprised. . . . He would always talk about what it would be like to stab someone but he would always gimme a weird look then laugh and say ‘just kidding.’ ”

Gayadeen said Aguilar would make these remarks in jest during spare time in a pre-engineering class, an elective they took to graduate. “He would be like, ‘I wonder what it feels like to stab someone. A knife piercing thru someone’s skin.’ ”

Christopher Berry, the principal of Blake, declined to comment.

But on Saturday at Zumiez at the Columbia mall, law enforcement authorities said Aguilar’s weapon of choice was a Mossberg 12-gauge shotgun.

Chu said Aguilar “mentioned about getting airsoft guns and a crossbow, but he never got them,” Chu said. “He just thinks weapons are interesting because [of how they are] engineered, but he talks about them for self-defense and home defense. . . . He was just into self defense because he cared about his loved ones.”

At Blake, Aguilar was not that well known. He wasn’t marginalized, though, his friends said, because many people were interested in his conversations. But Aguilar also sat at the same lunch table most days and remained quiet, opening up only “when there [were] less people at the table,” Chu said.

His favorite memory, Chu said, dates to the summer of 2012. The two had just finished up a day at the King Swim Center in Silver Spring and were walking back to his house along Route 29. But Chu got the cramps and fell down. “And [Aguilar] had to drag me to the side of the road, we shared a good laugh right there,” Chu recalled.

A Colorado woman who identified herself as Aguilar’s grandmother said in a brief interview that the news startled her.

“He was my spoiled little grandson. He wasn’t a bad kid. He was never in trouble,” she said. “You’re not supposed to bury your grandchildren.”

Alice Crites, Peter Hermann, Jennifer Jenkins, Dan Morse, Matt Zapotosky and Julie Zauzmer contributed to this report.