Student Tyanna Davis (R) and others place flowers outside Marysville-Pilchuck High School the day after a shooting at the school in Marysville, Washington October 25, 2014. [Photo/Agencies]

MARYSVILLE, Wash. - Authorities in Washington state worked on Saturday to find out what led a popular high school student to open fire on a group of classmates seated at a cafeteria table, killing one and wounding four others, including a pair of his cousins, before killing himself.

The Friday incident at Marysville-Pilchuck High School in the city of Marysville, north of Seattle, sent students fleeing from the building and sheltering under desks in the latest in a series of US school shootings.

The Snohomish County Sheriff's Office said on Saturday that officers had completed their on-scene investigation and recovered a 0.40 caliber handgun.

Police have not released the shooter's identity, but a Marysville school official and multiple classmates said a well-liked freshman named Jaylen Fryberg was responsible for Friday's rampage.

Students who knew Fryberg, a member of the Native American Tulalip Tribes, described him as an outgoing and popular football player, unlike the loner personality that is often associated with school shootings.

Authorities were also still piecing together a motive, interviewing about 100 witnesses, the sheriff's department said Saturday.

Classmates and parents said the teen shooter had recently been in a dispute on the football field and had also been despondent over a break up.

Rebecca Cooley, whose son played football with Fryberg, said he had recently been in a fight with another player over a disparaging remark made during football practice.

"(Jaylen) broke the kids nose," she said. "A lot of the football players stepped in during this fight," she said.

A school official who did not want to be named and a friend of one of the female victims said he had been recently rejected by a girl who favored his cousin.

"I heard he asked her out and she rebuffed him and was with his cousin," said Bella Panjeli, a ninth-grade student at a different school who said she was a friend of one female victim.

She added that she learned of the connection after talking to the victim's family and friends on social media. "It was a fight over a girl."

FRIENDS TARGETED

Witnesses said the shooter had targeted a single table in the cafeteria.

"He came up from behind and had a gun in his hand, and he fired about eight bullets," student Jordan Luton told CNN. " ... They were his friends so it wasn't just random."