A man said he woke up Tuesday and found the woman, who he knew, dead inside his apartment at Bear Street and Alton Avenue.
The man, 40-year-old Preet Grewal, was arrested on suspicion of murder. Authorities said his story didn't add up.
Authorities said firefighters responded to a 911 call for medical aid the man made at 10:30 a.m. When they arrived, they said they found a deceased woman in her 40s with signs of trauma on her body.
That's when police and homicide investigators were called to the scene. Grewal said he found the woman unconscious and in need of medical aid when he got up in the morning.
"Originally, we were told that the person who called did not know this woman," said Cpl. Anthony Bertagna of the Sana Ana Police Department. "We've now found out, through other folks, that in fact there is some type of relationship. Whether it be a friendship or a relationship between the two, we don't know. That's what we're looking into."
Police towed his convertible Audi to search for more evidence.
One neighbor said he heard loud music coming from Grewal's apartment Monday night, which caught his attention because it's usually a quiet complex.
Police said they planned to speak to residents in the area because it is a densely populated complex.
The woman's identity or cause of death has not yet been determined.
Anyone with information is asked to call Santa Ana police at (714) 245-8390.