Daniel Dieters, 25, called police around 11:10 p.m. Thursday to report he had just killed his friend, identified as 22-year-old Roy Kauwe.
When police arrived, Dieters was waiting in the parking lot of the Edgewood Apartments in the 400 block of Laguna Drive in Rohnert Park where Kauwe lived, Sgt. Jeff Justice said.
In the apartment police found Kauwe dead of multiple stab wounds in the neck area and a knife near his body, Justice said. Police haven't confirmed the knife is the murder weapon.
Police also contacted a 23-year-old woman who is associated with Kauwe and Dieters outside the apartment, Justice said.
The woman lived with Dieters and had been dating him for several years, but recently was seeing Kauwe, Justice said. She was aware there was tension between Dieters and Kauwe and went to Kauwe's apartment to check on both men, Justice said. Her name was not released.
Dieters was taken into custody, and the woman was brought to the public safety department for questioning, Justice said.
The woman said she arrived at the apartment just before Dieters called 911, Justice said. Police learned the murder occurred during a dispute over the relationship Dieters and Kauwe had with the woman, and Dieters gave police an account of what happened before he called 911.
Dieters was booked under no bail in the Sonoma County jail for homicide and is scheduled to be arraigned Tuesday afternoon in Sonoma County Superior Court. The woman was released after she was interviewed, Justice said.
Police said the investigation is ongoing.