Officers made the discovery while conducting a welfare check at an apartment complex on Parkmoor Avenue near Interstate 280.
Brandi Tomasovitch is house-sitting her sister's unit in the complex. When she came back from a hike in the morning she said at least 24 police vehicles were outside the complex.
"Four different officers were interviewing four different people you know there were tears so had to be family," Tomasovitch said.
She said residents received an email from property managers on Friday afternoon, it stated in part:
"Vista strives to make our community a safe place to call home. In consideration of this incident, we have hired a 24-hour security service to provide for the safety of our residents."
Residents like Yoseline Delariva describe the complex as relatively quiet with the occasional care break-ins or fireworks - nothing like this before.
"It's a pretty big shock to the community," Delariva said.
Police said no word on a suspect but said they will release information in the coming days.
"Just be protective over yourself and your loved ones cause anything like this can happen anytime," Delariva said.
The two victims were the 23rd and 24th homicides of the year, police said.