Fourth victim of US school shooting dies

A 15-year-old boy is the fourth victim to succumb to the injuries suffered two weeks ago when a high school student went on a shooting rampage in Washington state.

"Unfortunately, Andrew Fryberg, 15, passed away this evening," Harborview Medical Center in Seattle said.

The three other victims were all girls, one of whom died on the spot and two of whom died in hospital over the past two weeks. They had all been shot in the head.

The teen widely identified as the shooter, Jaylen Fryberg – reportedly a cousin of Andrew Fryberg – also turned the gun on himself.

In a brief statement Andrew Fryberg's family expressed gratitude "for the amazing support from the community, as well as from everyone around the world."

"Our family is overwhelmed with the love and care that has been provided to our loved one during this time and you all will forever hold a special place in our hearts," they said.

Police are attempting to ascertain a motive for the incident at Marysville-Pilchuck High School in Marysville, north of Seattle.

Jaylen Fryberg had left a series of tortured posts on Twitter, suggesting he was used to handling guns, and hinting that a failed romance may have led to the shooting.

Local media said Jaylen Fryberg, a Native American, played on the school football team and had been named a homecoming prince just a week before.