KELSO, Wash. (KOIN) — Several days after a man was found dead by the Cowlitz River, Kelso police announced they are officially ruling the case as a homicide.

Officers found the body — identified on Monday as 46-year-old Kelso resident Matthew H. Pettit — in a wooded area in the 400 block of N 1st Avenue on Thursday afternoon. The discovery of the body immediately spurred a “suspicious death” investigation.

Police say after performing an autopsy, the Cowlitz County Coroner’s Office determined that Pettit was killed and officially determined his death a homicide.

According to authorities, the specific cause of death is being withheld to preserve the integrity of the investigation.

Anyone with information believed to be helpful to the investigation is asked to contact Detective Slaven or Detective Christianson at 360-423-1270.