At about 9:35 p.m., officers responded to a residence in the 2200 block of Pinenut Way on report of gunfire, Antioch police Lt. Diane Aguinaga said in a statement.
Police said that a female resident called 911 after her ex-boyfriend showed up at her house, wielding a gun.
She told officers that she could hear shots being fired inside of her residence, according to Aguinaga.
Officers arrived at the scene and found a man suffering from multiple gunshot wounds. He was pronounced dead at the scene, Aguinaga said.
The woman's ex-boyfriend -- who police later identified as a 30-year-old Antioch resident -- fled the scene, but was found shortly after 12:30 a.m. on Tuesday in Antioch, Aguinaga said.
Police arrested the man and Aguinaga said that "no other suspects are outstanding."
Anyone with information about the incident is asked to call Antioch police Detective Castillo at (925) 779-6933.