MILL CREEK — A man who helped his son attack a 12-year-old boy at an apartment complex Wednesday evening has turned himself in to police.

Mill Creek police say Martinez D. Mitchell, 43, was booked into the Snohomish County Jail on Friday for first-degree assault on a child.

Officers responded shortly before 11:22 p.m. on Wednesday to a report of a stabbing at the Heatherwood Apartments in the 13500 block of North Creek Drive, according to a Mill Creek police news release. They found a boy who had been stabbed in the bicep, wrist and finger. He was transported to Harborview Medical Center in Seattle. His injuries were not believed to be life-threatening.

The boy told police Mitchell ran up to him, punched him and held him in place. Mitchell’s son, also 12, then allegedly punched and stabbed the boy.

Mitchell’s son was found at the apartment and was booked into the Denney Juvenile Justice Center in Everett for investigation of first-degree assault. He was released from detention on Thursday and placed on house arrest.

According to a police report filed in the son’s case, the two boys had been contacted by police several times in the past couple of months. Recently, an officer noted, both boys had been subject to eggings from one another. There were fresh splattered eggs found at both of the boys’ apartments on Wednesday.

Witnesses reported that Wednesday’s altercation may have been instigated by possible damage to a car.

A knife believed to be used in the attack was recovered at the scene.