The shooting happened about 6 p.m. inside an RV that was parked behind a home in the 26800 block of 172nd Place SE.
Officials said several people were in the RV where the man in his 20s was fatally shot.
Detectives interviewed at least four people before arresting the 26-year-old suspect. The victim and suspect have not been identified, but officials said the two knew each other.
It was not clear what prompted the shooting.