Police say it happened at Turing at the Fields Apartments in Milpitas, a luxury complex near the Great Mall.
A single bouquet of flowers sat outside the door of apartment 102 - a small sign of respect from a grieving neighbor following the tragedy.
Community members who work and live in this building were shocked and heartbroken.
"I'm very shocked considering it happened in Milpitas," Savannah Rae Dizon said. "I mean, nothing ever really happens in Milpitas."
"It's scary, you know," Jerry Saldana said. "We have a family, we've got children ourselves, and to think that we're just above the unit that it happened in and not knowing any information, it's concerning."
Milpitas police say family members said they had not heard from the family who lived here for several days.
A man, woman and two preteen children were found by officers with what police are calling "obvious signs of death," with no further details.
One neighbor told us a strong odor came from the apartment Tuesday night.
Saldana noticed the active scene Wednesday morning.
"When I came down, literally if the door was here, there was tape here and tape there and there was some furniture," Saldana said. "There was an office chair and some other random house items out and one officer out when I walked by."
MPD says there have been no other calls to this apartment in the past.
They could not confirm if a weapon was found or how the family died.
"At this time, all the evidence suggests it was an isolated incident and there's no ongoing threat to public safety," Lt. Tyler Jamison said. "This investigation is ongoing."
Neighbors say this is a new luxury apartment complex in a safe, quiet area.
The person who left the flowers said he would see the children playing in the courtyard frequently.
Saldana lives right up stairs. As a father himself, he can't believe this tragedy happened so close to the holidays.
"Gotta appreciate everyone and make sure you stay safe in your own home, I guess," Saldana said. "It's sad to think something like that happened so close. It breaks my heart."