Why did a popular student, athlete turn a gun on his classmates in Marysville?

MARYSVILLE, Wash. -- Seven days ago, the gunman in the Marysville Pilchuck High shooting was crowned homecoming prince: Jaylen Fryberg is seen in a YouTube clip happy and waving.

He was a popular kid before Friday's shooting rampage -- a teenager who has left behind many unanswered questions.

Witnesses say Fryberg, a freshman at Marysville Pilchuck High School, pulled a gun and without uttering a word opened fire in a crowded cafeteria, shooting five students, including two of his own cousins.

A family member tells Q13 FOX News that Fryberg kissed his mother goodbye Friday morning, like any other day, but his bullets sent his classmates scrambling.

"I will not promote the motivation by spending any time on the shooter," Marysville Police Chief Rick Smith said late Friday, refusing to even confirm the identity of the shooter. "It would simply dramatize someone who perpetuated a violent crime."

But many want to know why a well-liked athlete -- and a prominent member of the Tulalip Tribe -- would turn the gun on others before killing himself.

A family member says Fryberg got into a fight with some students, possibly one of his cousins, over a girl.

His Twitter page is riddled with emotional words. Three days ago he tweeted, "It breaks me...it actually does..i know it seems like i'm sweating it off...but i'm not and I never will be able to."

Then Thursday, his last tweet reads, "It wont last, it`ll never last."

Friday, people close to the tragedy were in pain -- and at a loss for why this happened.