(CNN) — A man accused of murdering 10 people at a Colorado grocery this week is scheduled to make his first court appearance Thursday morning, as investigators try to piece together a motive in the massacre.

Ahmad Al Aliwi Alissa, 21, is due to hear the charges against him in a Boulder court at 8:15 a.m. MT (10:15 a.m. ET), the county district attorney’s office said.

He is accused of opening fire outside and inside the King Soopers store Monday afternoon in the university town of Boulder, killing 10 people — including a police officer, store workers and shoppers — as numerous others fled or hid.

Alissa was arrested after he surrendered in the store that afternoon — with a gunshot wound to the leg — following a gunfire exchange with police, authorities said.

He faces 10 charges of murder in the first degree and one charge of attempted murder, according to a Boulder County arrest warrant.

It is unclear if Alissa will personally appear in court Thursday. A court document notes that he could waive his right to appear with a notice in writing.

The hearing is meant to advise Alissa of the charges he faces, his rights and the next court date in his case, the district attorney’s office said.

Authorities have said they’re still trying to determine a motive in the shooting. And they’re trying to figure out why the shooting happened in that particular location, a law enforcement official briefed on the investigation told CNN on condition of anonymity.

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Alissa’s home, in the Denver suburb of Arvada, is about 30 minutes from the store, and other grocery stores are closer to his residence, the official noted.

Investigators suspect the attack was planned, given that authorities say the suspect recently purchased a gun believed to have been used in the shooting, the official said. Investigators are also examining possible mental health questions, according to the official.

The FBI is looking at Alissa’s online activity and conducting interviews with friends and relatives, a law enforcement official told CNN, adding that Alissa was not previously the subject of any FBI investigation and it appears nothing in the federal system would have prohibited him from buying a firearm.

The attack began with a gunman shooting at least one man in the parking lot before entering the grocery store and opening fire.

The victims were: Boulder police Officer Eric Talley, 51; store manager Rikki Olds, 25; store employee Denny Stong, 20; store employee Teri Leiker, 51; Neven Stanisic, 23; Tralona “Lonna” Bartkowiak, 49; Suzanne Fountain, 59; Kevin Mahoney, 61; Lynn Murray, 62; and Jody Waters, 65.

Boulder Mayor Sam Weaver said Wednesday that he spoke with President Joe Biden, who expressed his condolences and sympathy.

“Of course, the conversation turned toward what can we do to make sure this never happens in another community in our country, and so we explored that a little bit,” the mayor told CNN’s Pamela Brown. “The President expressed that he regretted that when the first federal assault weapons ban was passed in 1994, that there had to be a 10-year sunset to get that through.

“He further regretted that the sunset occurred, and the ban expired. And then we talked some about what steps could be taken at the federal level to make sure that things like this just don’t happen to other communities.”

Vigils are held for the victims

The people of Boulder honored the victims on Wednesday as support poured in from public figures and citizens around the country.

Conversations in the community also have turned to how to prevent such a loss of life, especially following the mass shootings at three Atlanta-area massage spas that happened less than a week earlier.

Tribute was paid Wednesday to the heroism of Talley, the officer who lost his life at the scene, as people lined the streets Wednesday.

“It’s sad but glad we could honor his life,” Crystal Hootman told CNN. “I was talking with another resident and we both shop at the grocery store. I’m hoping out of sadness, Boulder becomes an even better place to live,” she said.

Talley’s body was transported to a funeral home in nearby Aurora, escorted by a procession of police and first responder vehicles.

At the King Soopers store, visitors left flowers and paid their respects Wednesday to the 10 people who died. Chaplains from churches were available to those in need, as well as Cubby, an emotional support golden retriever.

“They take on people’s feelings,” K-9 Crisis Response Coordinator for Lutheran Church Services Bonnie Fear told CNN affiliate KUSA. “We bring the dogs and bring comfort and smiles and just open up emotions for people so they can start the healing process.”

Store employees are remembered

Meanwhile, Bianca Porter, a friend of 20-year-old Denny Stong, the youngest victim in Monday’s shooting, said she wasn’t surprised to hear reports of Stong trying to protect others during the shooting.

“I had no doubt that he lost his life trying to save other people, that’s who he was,” she told CNN’s Erin Burnett Wednesday night.

She shared her favorite memory of Stong, a close friend of four years whom she had texted just an hour before the attack.

“Last year on my birthday, he was one of the only people that got me a birthday present, which made me feel very special,” Porter told Burnett. “He was really into aviation and stuff, so he brought his RC [radio controlled] plane and he was controlling it over the pond and just doing some really cool tricks with it. We were just all laughing and having a great time.”

Porter said Stong was dedicated to his work at the supermarket and had dreams of becoming a pilot.

“He was really passionate. Denny had a work ethic like no one else that I’ve ever met,” Porter said. “It’s not the most interesting job, but he looked forward to doing it, never once did I ever hear him complain about having to go into work late or something. He just really did what he could and had no complaints.”

The uncle of 25-year-old store manager Rikki Olds, a victim in Monday’s shooting, spoke about her personality at a press conference Wednesday.

“Rikki was kind of the light of our family,” Robert Olds said. “When Rikki showed up at the house, we never knew what color her hair was going to be, we never knew what new tattoos she may have.

“But that was Rikki and Rikki lived life on Rikki’s terms — not anybody else’s terms.”

Olds also said that “she had dreams, she had ambitions,” and praised her as “a strong, independent young woman.” She had planned to be a nurse, he said, but her attention turned to becoming a store manager at King Soopers.

Olds said that the outpouring of support has been “overwhelming,” adding that “It just goes to show how many lives that Rikki touched,” he said.

“She was a snorter when she laughed hard and I will really miss her,” he said. “I will really miss that personality of hers.”

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