FBI serves search warrant at Syed Farook's brother's home

CORONA, Calif. (KABC) -- The FBI says agents served a search warrant at the home of San Bernardino shooter Syed Farook's brother on Thursday.

The search, which took place in Corona, netted no arrests, but the FBI says Farook's father was detained for his own safety.

Agents spent around four hours at the home and were seen taking a computer and dozens of manila folders. They also took some type of heavy equipment that appeared to have a metal frame and a crank on the side.

The home is the residence of Farook's brother, Syed Raheel Farook. Neighbors say Syed Raheel Farook lives in the home with his wife and young daughter.

MORE: Apple ordered to help FBI hack San Bernardino killer's phone

Recently, neighbors say Syed Raheel Farook's mother has spent a lot of time at the home. A black Lexus parked on the driveway is registered to her. Agents looked through the vehicle, specifically the trunk, and even took off the spare tire cover to search underneath it.

Neighbors said this is approximately the fourth time the FBI has served search warrants at the home.

"It's a big deal and hopefully if Raheel knows something, that he could help out if he can. I'm just hoping that they are not part of it because they seem like a very nice, normal family," said Stacy Mozer, a neighbor.

MORE: Apple encryption battle draws in Silicon Valley heavyweights

Syed Farook and his wife, Tashfeen Malik, killed 14 people in a December attack at the Inland Regional Center. The two were killed in a gun battle with authorities.

The FBI confirmed to ABC News that it has not ruled out the possibility of that their might have been a third shooter in the attack. But the FBI said evidence suggests only two weapons were fired during the attack.

MORE: FBI hasn't ruled out third shooter in San Bernardino terrorist attack

The Thursday morning raid comes just days after the FBI legally challenged Apple to grant them access to Farook's iPhone.

The FBI has had his phone for two months but can't gain access.

The government is asking that Apple be ordered to provide a software file to bypass or disable the auto-erase function.

MORE: San Bernardino terror attack victims' families ask Apple to cooperate with FBI

Apple CEO Tim Cook says the order from a federal magistrate could threaten the security of millions of iPhones.

Cook also said the software would be too dangerous, and once created, it could be used repeatedly on other devices.

Syed Raheel Farook was in the Navy from 2003 to 2007, military records show. During his stint, he received the Global War on Terrorism Expeditionary Medal and the Global War on Terrorism Service Medal, among other awards.

After going through training in the family's native Illinois, Syed Raheel Farook served for three years aboard the aircraft carrier USS Enterprise as an information system technician.

The Associated Press contributed to this report.