ORANGE, Calif. (Reuters) — One of the four victims killed in a shooting rampage in Orange County, California on Wednesday was a 9-year-old boy who apparently died in his wounded mother’s arms as she tried in vain to save him, officials said on Thursday.

“It appears that a little boy died in his mother’s arms as she was trying to save him during this horrific massacre,” Orange County District Attorney Todd Spitzer told a news conference.

The bloodshed in Orange, California, about 30 miles southeast of central Los Angeles, marked the third deadly mass shooting in the United States in less than a month.

In the two other incidents in March, a man killed eight people including six Asian women at three Atlanta-area spas, and another man opened fire at a supermarket in Boulder, Colorado, killing 10.

Unlike the other two outbursts, investigators in California say they were able to determine immediately that the shooter knew the victims, ruling out a random act of violence.

“The preliminary motive is believed to be related to a business and personal relationship which existed between the suspect and all of the victims,” Orange Police Department Lieutenant Jennifer Amat told the same news conference.

Officials identified the suspect as Aminadab Gaxiola Gonzalez, 44, a resident of the nearby city of Fullerton.

Besides the boy, the other fatalities were a man and two women.

The shooter and the woman who was protecting the boy both remained hospitalized in critical but stable condition, Amat said.

On Wednesday afternoon, the suspect entered the office complex of a business called Unified Homes that buys and sells mobile home and locked the gates to a courtyard behind him with bicycle locks, police said.

Shots were still being fired when officers arrived, officials said, but they were locked out until they could sever the chains with bolt cutters.

“In the meantime, horrific rampage was going on in offices and people were dying or were being shot,” Spitzer said.

From outside the courtyard, two of the officers engaged in a gunbattle with the suspect, who was wounded and arrested, Amat said.

Authorities recovered a semi-automatic handgun and a backpack containing pepper spray, handcuffs and ammunition that they believe belonged to the suspect.

After aiding the wounded woman who appeared to be protecting the dead 9-year-old-boy, police searched the complex and found a dead woman on an upstairs outdoor landing, a dead man inside an office building, and a dead woman in another office building, Amat said.

Police are withholding their identities until relatives can be notified.

(Reporting by Daniel Trotta in Vista, California; editing by Jonathan Oatis and Marguerita Choy)