Correction: An earlier version of this story misspelled Brianna Benlolo’s name. This version has been updated.

On the final morning of his short life, Darion Marcus Aguilar climbed into a taxi in Burtonsville, 10 miles north of his College Park home. He carried a backpack and a pump-action, pistol-grip shotgun, a Mossberg 12-gauge, which he kept hidden as he informed the driver where he wanted to go.

The Mall in Columbia, he told the cabbie.

Just 19 years old, a 2013 graduate of James Hubert Blake High School in Silver Spring, Aguilar had been scheduled to work early Saturday, at a Dunkin’ Donuts. He didn’t show up. And by day’s end — hours after his violent, self-
inflicted demise — his mother, having tried again and again to reach him, would report him missing to the police.

Under a sunless sky, gray and frigid, it was about 10 a.m. as the taxi cruised north to Howard County. Soon, Aguilar — who kept a journal, in which he wrote of his dissatisfaction with his life, according to police — would fatally shoot two employees of a clothing shop, spreading terror in a suburban mall packed with shoppers.

Then he would turn the Mossberg on himself.

Darion Marcus Aguilar, 19, of College Park, in his Junior year, yearbook photo. He went to James Hubert Blake High School in Silver Spring, Md. (Photo by Lifetouch)

But why?

Sunday night, almost 36 hours after the shootings, after “a considerable amount of time interviewing families, friends, associates of our victims and our shooter,” investigators still had not uncovered a motive for the attack, Howard County Police Chief William J. McMahon said. He said they had found no connections between Aguilar and either of the young adults he killed, Brianna Benlolo and Tyler Johnson.

Benlolo, 21, of College Park, and Johnson, 25, of Mount Airy, worked together in Zumiez, a store for skateboarders, snowboarders and surfers. Although police said they have found no evidence that Benlolo and Aguilar were acquainted, Benlolo and Aguilar lived a short distance apart.

“There’s still speculation that there was somehow some romantic involvement” between Aguilar and Benlolo and Johnson and Benlolo, McMahon said. “We have not been able to establish that, and I’m not sure where that information is coming from. And it’s becoming very frustrating for the families of the victims to hear this.”

The apparent absence of a relationship between them and their killer adds a layer of mystery to the mayhem. If Aguilar didn’t travel to the mall specifically to shoot Benlolo or Johnson, if his purpose was random murder, why did he stop so soon, with only two victims dead? He had abundant ammo, authorities said. Why didn’t he keep shooting until the police arrived, until they cornered him or gunned him down?

These tragedies are familiar by now, and that’s how they normally end.

“We don’t know why,” said Howard County Executive Ken Ulman.

How it began: The cab pulled up at an upper-level entrance to the mall, near a Sears and a Starbucks, at about 10:15 a.m., just after the mall opened, Ulman said. In view of a surveillance camera, Aguilar got out, toting his backpack, and walked calmly through the doors.

Ahead of him as he entered, in a central area of the mall, was a merry-go-round, which is usually spinning with children. He strolled past it, stepping onto an escalator near the carousel. At the bottom of the escalator, on the first level, is the food court. Under the eye of another video camera, he lingered for about an hour, sitting, standing, pacing, Ulman said.

“We don’t have him on camera in the food court the entire time,” Ulman said. “But we know he stayed in that area because we would know if he moved out of that area. . . . The way the cameras are, we would have seen him somewhere else if he left that area.”

Investigators “don’t know where the weapon was,” Ulman said. The shotgun was new to Aguilar; he bought it last month in Montgomery County, police said. “The assumption is it was in the backpack,” Ulman said. “It certainly wasn’t visible. He wasn’t carrying it openly.”

Then, about 11:15, Aguilar got back on the escalator and rode up. As he got off, the Zumiez store was just steps away. Benlolo and Johnson were the only workers, police said. There was one customer in the store, browsing.

Aguilar apparently walked through the store and entered a dressing room near the back, Ulman said, because the dressing room is where police would later find his backpack, containing a crude, low-grade explosive device made with firecrackers.

Just seconds went by, evidently, before he emerged from the dressing room wielding the loaded shotgun.

“We heard a loud bang,” said Courtney Birkmeyer, 22, who was with her mother in an American Eagle Outfitters store, trying on clothes.

“We thought it might be a clothing rack falling over.”

Seconds later, the two heard more booms, and realized they were gunshots. “Survival mode took over,” Birkmeyer said. “We got into the dressing room as quick as we could, and we crouched on the little bench where you can rest your garments — so our feet weren’t seen, just in case someone was walking around.”

Ulman said police think Aguilar fired six to eight rounds with the Mossberg, using the final round on himself. Like his victims, he died on the floor of Zumiez. The customer in the store suffered no harm, police said.

Birkmeyer said she spoke with her father by cellphone during her and her mother’s harrowing 80 minutes in the dressing room. He was in another part of the mall, near the lower level food court, and kept his family updated with what was going on.

Arriving within minutes, heavily armed police officers swarmed through the mall, looking for a possible accomplice of the gunman, while hundreds of patrons fled to the icy cold outside. Five people needed medical treatment. One of them, who was outside the store, was hit by stray buckshot from the gun and suffered a minor wound, police said. The others incurred small injuries in the frantic mass exodus from the shopping complex.

As for Birkmeyer, “we were kind of safe and contained in our little dressing room,” she said. “So the panic was setting in. But luckily we didn’t have any of the visuals.”

Brandon Cole, 36, of Greenbelt, said he had just taken his 19-month-old daughter’s shoes off so she could run in a play area in the lower level of the mall.

He and his wife, Taylor Cole, were standing behind a bench watching their little girl play.

“We were sitting there quietly, admiring our young baby daughter and the innocent joy that is childhood,” he said. “And I heard two loud booms.”

Then he heard another. “I said: ‘That’s a gun! . . . We need to move! We need to get out of here!’ ” Cole, who works for the Army, said he vaulted over a wall as his wife grabbed their child. They hurried into a J.C. Penney store and eventually out of the mall.

“I saw the threat, assessed and moved,” Cole said. “I just reacted; I didn’t think.”

He said: “I was never scared. And I really only was overcome by emotion when I knew we were safe, and I was able to put hands on my wife and daughter, and just know how close we were to being injured or hurt.”

Meanwhile, back in College Park, Aguilar’s mother, having been unable to reach him, phoned Prince George’s County police to report him missing. They two lived together in a two-story white house in the 4700 block of Hollywood Road. At the house, officers inspected Aguilar’s journal and saw notations that made them realize he might have been a threat to himself.

“The investigator began to actively search for the missing man, to include tracking his phone,” police said in a missing persons report. “The phone indicated it was in the Columbia area, and our investigator soon determined it was pinging at the Mall in Columbia.”

Prince George’s officers arrived at the mall shortly before 6 p.m. “Not long thereafter, it was confirmed the missing person and the deceased gunman were one and the same.”

Referring to Aguilar’s journal at a news briefing Sunday night, Chief McMahon offered few details of the gunman’s musings, describing only his theme: “He does express some general unhappiness with his life.”

Matt Zapotosky, Julie Zauzmer and Dan Morse contributed to this report.