Investigators say that a gunman responsible for a shooting at a Washington state high school on Friday invited his victims to lunch by text message.

Snohomish County Sheriff Ty Trenary told a news conference Monday the five students were all at a lunch table when they were shot by 15-year-old Jaylen Fryberg.

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 sheriff said investigators continue combing through a massive amount of text messages, phone records and social media posts as they search for an explanation for the shooting _ but he also says they may never find one.

Two 14-year-old girls were killed, and three students remain hospitalized. Fryberg also killed himself. Trenary said that while a teacher tried to intervene, she did not have any physical contact with the gunman before he killed himself.

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