At 8:47 a.m., Chula Vista police officers were called to reports of shots fired at the Pinnacle Apartment complex in the 1300 block of Santa Rita.
When they arrived, they found the victim with a gunshot to his chest, police said. First responders tried to revive him but he was pronounced dead at the scene.
Melissa Hayes-Spencer, 30, told police that she shot the man because he was hitting her. According to police, she was cooperative and willingly went to the station for questioning. However, at 8:30 p.m., authorities booked and arrested her for homicide.
Police said that they found no signs of struggle, just a minor scratch on the woman's hand. The body was taken to the San Diego County Medical Examiner's office for further investigation.
The two had lived in the apartment for a little more than a month and there were no records of domestic dispute calls at the residence, according to police.
Police said a gun was recovered at the scene.