A 44-year-old man suspected of opening fire inside a Southern California office building locked gates to the property's entrance before the attack that left four people dead, including a 9-year-old boy.
A fifth victim and the suspected shooter, identified by police Thursday as 44-year-old Aminadab Galaxio-Gonzalez, of Fullerton, remained hospitalized. The victims all had personal and business connections with the suspect, but authorities did not provide more details at a Thursday news conference.
"This was not a random act of violence," Orange Police Lt. Jennifer Amat said Thursday. "We believe everyone knew each other, whether through a business or personal relationship."
While police withheld the identities of the victims, the son of one of the victims, Luis Tovar, told NBCLA his father Luis senior is among the dead.
Friends said Tovar had just celebrated his 50th birthday -- a man described by his son as a giver.
"He was a hardworking guy. Always family first. Always put others in front of himself type of guy," he said.
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Tovar told NBCLA his mother Blanca was also shot and killed along with his half brother, 9-year-old Matthew. A fourth victim was a female co-worker.
"She was super loving, very loving mom. Same as dad -- she put others in front of her ," Tovar said.
The fifth person was Tovar’s sister, Genevive, who was rushed to the hospital. She remains critical along with the suspect.
It was not immediately clear whether the suspected shooter was struck by gunfire from officers or his wounds were self-inflicted.
A semi-automatic handgun, pepper spray, handcuffs and ammunition were found in a backpack at the scene in Orange, police said. Investigators also provided chilling details about what officers, who opened fire on the shooter, encountered when they arrived at the scene in the 200 block of West Lincoln Avenue around 5:30 p.m. as shots were being fired.
Police say they were on scene within two minutes of the first 911 calls.
Officials later Thursday also released a shocking surveillance image from the day of the shooting, showing the armed suspect inside of the building.
Gates to the property and been chained from the inside with a bicycle lock to prevent officers from entering, police said. Officers used a bolt cutter to break the locks as they rushed toward the gunfire.
Alec Torres, who owns a business at the complex, said the shooter likely was familiar with the property.
“I believe the shooter was familiar with the building,” Torres said. “He closed the front gate to the entrance, which would not allow anybody to leave.”
A woman and 9-year-old Matthew were found in the courtyard. The boy, believed to be the woman's son, was dead, with District Attorney Todd Spitzer saying he died in his mother's arms.
Other victims were found in office suites. Amat said the shooting happened on both levels of the building.
"The preliminary motive is believed to be related to a personal or business relationship," Amat said.
Signs outside indicated a handful of businesses are located there — including an insurance office, a financial consulting firm, a legal services business and a phone repair store.
The violence was the third U.S. mass shooting in just over two weeks.
California Gov. Gavin Newsom in a tweet called the killings “horrifying and heartbreaking.”
“Our hearts are with the families impacted by this terrible tragedy tonight,” he said.
The killings followed a mass shooting at a supermarket in Boulder, Colorado, last week that left 10 dead. A week before that, six Asian women were among eight people killed at three Atlanta-area spas.
Vikki Vargas contributed to this story.