April 1 (Reuters) - The shooting in Orange, California, that killed four people including a 9-year-old boy on Wednesday was carried out by a 44-year-old man who knew the victims, police said on Thursday, as they ruled out the shooting as a random act.

Besides the boy, the other fatalities were a man and two women, Orange Police Department Lieutenant Jennifer Amat told a news conference. Another woman and the shooter were hospitalized, Amat said.

Officials identified the suspect as Aminadab Gaxiola Gonzalez, 44, a resident of the nearby city of Fullerton, saying he entered an office complex of a business called Unified Homes on Wednesday afternoon and locked the gates to a courtyard behind him with a bicycle lock.

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

"The preliminary motive is believed to be related to a business and personal relationship which existed between the suspect and all of the victims. It appears all of the adults were connected either by business or a personal relationship and this was not a random act of violence," Amat said.

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Shots were still being fired when officers arrived at the scene, but they could not enter the courtyard until they forced their way through the lock, the lieutenant said.

Two of the officers engaged in a gunbattle with the suspect, who was wounded and arrested, Amat said.

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

Police are withholding their identities until relatives can be notified.

The bloodshed in the city of Orange, about 30 miles (48 km)southeast of downtown Los Angeles, marked the third deadly mass shooting in the United States in less than a month.

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