Three young adults were fatally shot and killed, and a fourth was injured early Saturday, July 30 at an upscale neighborhood in Mukilteo, Washington, a waterfront town of about 20,000 people, 25 miles north of Seattle.

About 15 to 20 teenagers and young adults were gathered for a party before the suspect walked in and started shooting. Neighbors told NBC that they heard 10 to 12 shots go off.

According to NBC News, a 19-year-old suspect, Allen Christopher Ivanov, is in custody, being booked on three counts of murder, including one count of aggravated murder. CBS News reports state troopers pulled over and arrested Ivanov on an interstate more than 100 miles away.

A witness says she saw the gunman enter the house with a rifle and walked out to the fire pit in back where he shot two victims. The ones present who knew Ivanov said he and one of the victims had recently broken up the week before.

Hundreds of young people and families gathered Saturday night at Mukilteo’s Kamiak High School who are devastated by this tragedy. The Seattle Times covered the event, and captured photos of friends and family mourning in the school parking lot.