MARYSVILLE, Wash. >> A popular student responsible for a shooting at a Washington state high school on Friday invited his victims to lunch by text message, then shot them at their table, investigators said Monday.

Snohomish County Sheriff Ty Trenary said at a news conference that the five students were at a lunch table when they were shot by 15-year-old Jaylen Fryberg. Fryberg then committed suicide.

Detectives are digging through reams of text messages, phone and social media records as part of an investigation that could take months, Trenary said.

“The question everybody wants is, ‘Why?'” Trenary said. “I don’t know that the ‘why’ is something we can provide.”

Fryberg, a football player who was named a prince on the school’s Homecoming court one week before the killings, was a member of a prominent Tulalip Indian Tribes family. He seemed happy although he was also upset about a girl, friends said. His Twitter feed was recently full of vague, anguished postings, like “It won’t last … It’ll never last,” and “I should have listened. … You were right … The whole time you were right.”

On Friday, after texting five friends to invite them to lunch, he pulled out a handgun in the cafeteria and started shooting. The victims were Zoe R. Galasso, 14, who died at the scene; Gia Soriano, 14, who died at a hospital Sunday night; Shaylee Chuckulnaskit, 14, who remains in critical condition; and his two cousins, Nate Hatch, 14, and Andrew Fryberg, 15.

Hatch, who was shot in the jaw, is the only victim who has shown improvement. He was upgraded to satisfactory condition Monday in intensive care at Harborview Medical Center in Seattle, while Andrew Fryberg remained in critical condition there.

Soriano’s family said her organs would be donated.

“We are devastated by this senseless tragedy,” her family said in a statement, read at a news conference by Providence Regional Medical Center’s Dr. Joanne Roberts. “Gia is our beautiful daughter, and words cannot express how much we will miss her.”

Trenary also confirmed that the .40-caliber handgun used in the shooting had been legally purchased by one of Fryberg’s relatives. It remains unclear how Fryberg obtained the weapon.

The Snohomish County Medical Examiner on Monday ruled Fryberg’s death a suicide. There had been some question over whether he might have shot himself accidentally as a teacher tried to intervene, but Trenary said Monday that investigators confirmed there was no physical contact between the teacher and the gunman.

At the memorial outside the school Monday, a group of mourners hugged each other tightly at 10:39 a.m. — the minute the shooting was reported Friday. Flowers and signs were zip-tied to a chain-link fence lined with red and white balloons reflecting the school’s colors. Many referenced the victims and said they’d be missed.

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Johnson reported from Seattle.