One of the victims was reportedly the alleged gunmans ex girlfriend.
A relative of a witness told NBC that one of the victims was reportedly the alleged gunman's ex girlfriend. Jaromir Chalabala/Shutterstock

A shooter fired into a party of 15 to 20 teenagers and young adults last night, KING 5 reports. Three people are dead, and one has been injured and is being treated at Harborview.

Here's more from NBC:

Susan Gemmer told The Associated Press that her 18-year-old granddaughter, Alexis Gemmer, hid in a closet to escape the gunman. She was hanging out with friends from Kamiak High School at the home in Mukilteo when a young man showed up with a rifle.

Gemmer said that according to her granddaughter, the gunman shot two people at a fire pit before going onto a roof and firing more shots from there.

The identity of the 19-year-old suspect has not yet been released. We'll update when there's more.

UPDATE: The suspect, identified Allen Christopher Ivanov, was arrested and booked into Snohomish County Jail Saturday afternoon. He has not yet been charged and is expected to appear in court Monday.

The Seattle Times covered a Saturday night vigil for the victims, whom friends identified as Anna Bui, Jake Long, and Jordan Ebner. Ivanov is reportedly a student at the University of Washington. A friend told the Times Bui and Ivanov dated.