CNN  — 

When police were finally able to enter the courtyard of the business complex in Orange, California – where four people were fatally shot Wednesday – they found a woman holding a wounded 9-year-old boy.

“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 said at a news conference Thursday, though he later added the exact nature of their relationship was still under investigation.

The killings marked at least the 20th mass shooting since the attacks at Atlanta-area spas two weeks ago. Although investigations are still underway, police have begun to uncover what happened behind the locked gates of the courtyard, where the doors into the suites are, as well as what led up to the horrific 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 spokesperson Lt. Jennifer Amat said in a news conference Thursday.

“This was not a random act of violence,” she said.

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.

When they arrived, they heard shots being fired inside, but they were not able to enter immediately. From the inside, gates to the building’s courtyard were locked “using a bicycle-type cable lock,” Amat said.

It is unclear if they were meant to keep the victims inside or officers out, police officials said.

Police tape cordons off the building where the shooting occurred.

What police found when they entered

After engaging with the suspect and firing shots, police used bolt cutters to enter the courtyard and found the suspect, who was injured, and took him into custody. Police had earlier said it was unclear whether his injury was self-inflicted.

In the courtyard, police also found the boy and the adult woman who survived. She was taken to a local hospital, where she is in critical but stable condition, Amat said.

Besides the boy, those killed were two women and a man, Amat said.

One of the women was found upstairs on an outdoor landing. The man was found inside one office building, and the other woman was found in a separate office building, according to Amat.

The suites where some victims were found belonged to a business identified as Unified Homes, Amat said, a real estate business specializing in mobile homes.

Investigators recovered a semi-automatic handgun and a backpack containing pepper spray, handcuffs and ammunition, which authorities believe belonged to the suspect.

Orange police and detectives gather at the entrance to 202 West Lincoln Avenue.

The victims

The Orange Police Department on Friday identified the four victims as Matthew Farias, 9; Jenevieve Raygoza, 28; Leticia Solis Guzman, 58; and Luis Tovar, 50.

“Our condolences go out to all of the victims and their loved ones,” the department said in