Los Angeles resident Harold Yong Park was arrested and booked for investigation of murder by Los Angeles County Sheriff's Department investigators. He was held without bail.
Police said Park had multiple pounds of marijuana with him when he was arrested. The marijuana is suspected of being stolen from the West Hollywood apartment where three murders occurred Thursday.
The bodies of Pirooz Moussazadeh, 27, his brother Shahriar Moussazadeh, 38, and Bernard Khalili 27 were all found lying facing down in apartment 204.
"Detectives do believe that robbery was a motive for the murders," said sheriff's Dep. Lillian Peck. "Immediately following the murders, several pounds of marijuana were taken, and that marijuana was located inside the vehicle."
Authorities won't say if they are looking for other suspects.
People in the quiet neighborhood said they were relieved a suspect was caught.
"Oh, my God, I'm so relieved," said neighbor Maurice Chiriqui. "Just to know that they finally have him. My wife wouldn't stay home alone. My neighbors across the street were not at ease because we never know what could happen."
The Associated Press contributed to this report.