An 18-year-old from Chandler was arrested on suspicion of fatally shooting his girlfriend in his bedroom and fleeing to a motel room in Mesa.
Police say Eric Coulter shot 18-year-old Monique Cota on Saturday night and then fled to the motel, where he was later found with his sister and brother.
Cota was shot, point blank, in the forehead.
Investigators say Coulter had assaulted Cota two days earlier -- and the two had a history of domestic violence.
The two were also arrested for domestic violence last October.
About a month ago, records show Cota left Coulter after he tampered with her car, causing damage. She got back together with a former boyfriend -- got engaged -- and had planned to move to California.
At first, Coulter claimed the shooting was an accident that occurred as he was inspecting an AR-15 rifle.
Right after the killing -- Coulter's sister Melissa Smith is accused of taking two guns from Coulter's bedroom and hiding them in the neighbor's bushes. Officers say she also hid a shotgun at her brother John's home in Phoenix.
Smith then allegedly drove Eric Coulter to the motel room in Mesa.
John Coulter was booked on charges of marijuana possession and forgery. Police say he was in possession of two New York ID cards, with Eric's photo on them.
Melissa Smith was booked on hindering prosecution, obstructing a criminal investigation, and tampering with evidence.
Investigators also found ammunition and $2,000 in cash in the motel room.
Eric Coulter's bond was set at $1 million.
Follow this story: Chandler Man Arrested After Girlfriend Murdered