The victims included a 51-year-old police officer, who was one of the first to respond to the scene.
Police went on to conduct a "systematic search" of the complex, and they found three more victims, all of whom were deceased: a woman "upstairs on an outdoor landing", a man inside an office, and a woman inside another office.
"Our hearts are with the families impacted by this awful tragedy tonight", he said.
Prosecutors are also looking into whether the fact that the gates were locked constitutes 'lying in wait, ' Spitzer said, a special circumstance that would also make the suspect eligible for the death penalty.
US Representative Katie Porter from California also tweeted, saying: "I'm deeply saddened by reports of a mass shooting in Orange County, and I'm continuing to keep victims and their loved ones in my thoughts as we continue to learn more". On March 22, a man stormed a grocery store in Boulder and killed 10 people.
© Orange Police Department This undated photo provided by the Orange Police Department shows Aminadab Gaxiola Gonzalez, a 44-year-old Fullerton, Calif., who is the suspect in a shooting that occurred inside a business in Orange, Calif., on March 31, 2021. It was unclear whether he suffered a self-inflicted wound or was shot by police. They said the precise relationships were still being determined and no names of the victims have been released.
Five calls to 911 came in around 5:34 p.m., Amat said, and officers were at the complex about 30 miles south of Los Angeles about two minutes later.
Amat said Wednesday night the city had not seen such violence since 1997.
When they arrived, they heard shots being fired inside, but they were not able to enter immediately.
Authorities also disclosed that the suspected gunman in Wednesday's violence, who was himself wounded before he was taken into custody, knew all of his victims and had a family relationship with at least one of them. Another woman and the shooter were hospitalized, Amat said.
Tim Smith's home is separated from the office's parking lot by a backyard wooden fence.
"Asking a jury to pass down a verdict of death is the most serious effect we ask, and it's the only outcome where a jury makes the decision as opposed to a judge", he said.
Police said Gonzalez knew all the victims either personally or through business.
Then Madrigal heard about 10 shots, followed by silence. He later peeked over the fence and saw SWAT officers marching in a line in the building's courtyard.
"Our hearts are shattered into a million pieces as the community mourns the loss of four innocent lives, including a young boy, as a result of the horrific events that unfolded Wednesday evening and we pray for the recovery of the sole survivor", Spitzer said in a statement Friday.
Police said the alleged shooter apparently targeted the office suites of a company called Unified Homes, a mobile home brokerage.
"He's not answering his phone, neither's my niece", Tovar said. "I'm pretty scared and anxious. right now I'm just praying really hard".
"The residents of Orange County can rest assured that the District Attorney's Office is taking every possible step to ensure that every aspect of this case and the subsequent officer-involved shooting is thoroughly reviewed and that justice will be served for each and every victim", he added.
Scott Clark, owner of Calco Financial, left his office early on Wednesday, around 4.45 pm. His workplace is two doors down from Unified Homes.
He said he's worked out of the building for about 21-years and Unified Homes has been in that location for seven or eight years.
He was living in a motel in Anaheim, northwest of Orange, and used a rental auto to get to Unified Homes, Amat said. He said he's chatted with the owner, sometimes inviting him inside his own office to take a break.
"He works so hard".