The 54-year-old is the second suspect arrested in connection with the death. A 28-year-old Mount Vernon man was arrested about three hours after the discovery of the body in the parking lot of a Haggens Grocery Store.
Police have not yet identified either suspect, but earlier said they were seeking a Francisco Castillo who is about 54 years old. Investigators have not confirmed this as his true identity but said he has used the name for employment purposes in Skagit County.
Two Mount Vernon detectives flew to Los Angeles this week to confirm the identity of the 54-year-old suspect arrested there. He is being held in California on suspicion of second-degree manslaughter, and will be extradited to Washington once court paperwork is complete, said Lt. Chris Cammock of the Mount Vernon police.
The investigation originally began March 25 at about 10:30 p.m. when police received a call about shots fired in the 300 block of Anderson Road in Mount Vernon.
Officers responded to that call but didn't find anything suspicious. The next day, a man who lives in that area called police to say he had found blood in his house, which he shares with several people.
Mount Vernon police began looking for a car associated with that house and also asked Arlington police to be on the lookout for the vehicle. Police say the car they were looking for is the same car found three days later with a body inside it.
Further investigation led them to the 28-year-old Mount Vernon man, who was believed to be with the victim Monday night at the time shots were fired. He was booked into Skagit County Jail for investigation of second-degree manslaughter.
Police believe the 54-year-old suspect arrested this week also was with the victim at the time shots were fired. The name of the victim has not been released.
Evidence collected by investigators indicates a shooting occurred at the Anderson Road residence, however the circumstances surrounding what occurred is still under investigation.
Anyone with information is asked to call the Mount Vernon Police Department's Criminal Investigations Division at (360) 336-6271 or the tip line at (360) 336-0632.