Yakima County sheriff's office says the 18-year-old has been booked in county jail on suspicion of first-degree assault. The 26-year-old uncle is in critical but stable condition at a Yakima hospital.
The Yakima Herald-Republic reports Friday's shooting took place at the Harrah home where both men live.
On Saturday, Sgt. Mike Russell said the suspect initially told investigators that he shot his uncle while attempting to commit suicide. Upon further investigating, investigators learned that the suspect was frustrated because the victim did not want to maintain an "intimate relationship."