The domestic mass shooting happened at the 400 block of Kitty Hawk Road in Alameda.
The suspect is in custody, and police believe he shot and killed his wife, father-in-law, mother-in-law, and his 6-year-old son. He also shot his second son, a 1-year-old who is critically injured. The motive is still under investigation.
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Police arrived at the home after getting a call from a neighbor. Officers saw one of the victims out front and then the suspect soon after that.
"Officers were in front of the residence providing aid to father-in-law. Then he came out of the front door of his residence," said Alameda Police Chief Nishant Joshi.
Police say the suspect did not resist arrest.
Alameda police recovered multiple guns with "significant evidence."
"This is a tragic and sad incident, and I'll say this, these are the actions of a coward," said Chief Joshi.
Chief Joshi said this is emotional and hard for the police department.
"Our officers are hurt, they're professionals but they're also human beings," Chief Joshi said. "They are doing the best they can but they're going to stay focused on making sure this family sees the justice they deserve."
Neighbors are shaken up by this tragedy. Some told ABC7 News they heard gunshots Wednesday night but thought it was fireworks left over from the 4th of July.
Unfortunately, it was much more gruesome than that.
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"I raised my kids here, I'm a mom, I'm a grandmother," said neighbor Deborah Wright. "You can't process how that happens and I can't. It's too much."
"It's pretty, pretty unbelievable," another neighbor Ashraf Elnakhal said. "We take for granted our safety here. We go out for walks early in the morning. We live with our family, we know our neighbors. To know that this type of violence took place here is pretty, pretty scary."
"It's heartbreaking. I can't really comprehend that he's gone," said next door neighbor Diane. "Our kids played together you know. I don't know how I'm going to tell my 3-year-old when he asks where his friend is?"
According to Diane, her son would play with the 6-year-old and 1-year-old.
"They loved riding their bikes up and down. They'd push the little one in the car. They'd run back and forth between houses," said Diane.
Neighbors say the family moved to that home last November or December.
One neighbor told ABC7 News that the suspect worked in construction as a welder and that he spoke Spanish pretty well. The suspect's wife and family were originally from El Salvador, according to the neighbor.
"He took to his family's Spanish-speaking culture; he was practically fluent. I'm at a loss - what happened?" said a neighbor who identified himself as Chris.
The community still can't believe the tragic turn of events.
"It's unbelievable. There are so many things I would imagine that make it hard to get to where we are now - for this to happen," said Diane. "You'd imagine at some point you'd stop and say 'What am I doing? Why am i doing this?' It never got there."
Mourning Alameda community hosts vigil
As the sun set over the beaches of Alameda Thursday night, over a dozen friends and neighbors came out to remember.
One man who identified himself as Coach Ray, came out to the beach Thursday evening.
Ray says he lives nearby and thought the gunshots he heard were fireworks.
"I heard it. It was like 9:30, 10 o'clock. I didn't pay any attention to it. And when I got home is when everything started going past us," said Ray.
Throughout the day on Thursday, many came from around Alameda to visit the house. Some stopping to pray - others leaving flowers or gifts.
Coach Ray, who is involved with little league baseball on the island, tells us he left a baseball bat and game ball for the 6-year-old.
"I gave him a game ball because every kid gets a game ball. You try as hard as you can to make sure every kid gets a game ball. And he's never going to get that," he said.
Mike Devine organized Thursday's vigil. He says news of the shooting has sent shockwaves through this normally quiet and tight-knit community.
"I think people think of Alameda as a safe community. We have the same risks of this kind of thing that every other community in America has," Devine said.
Justice for the family and also a community in mourning.
"I have two kids and I would never in my life... no matter what's happening, would I think of. I don't know what's behind it, if anything, but it blows my mind," Coach Ray said.