SAN GABRIEL (CBSLA.com) — A Pomona SWAT officer was shot Tuesday morning while serving a search warrant at a San Gabriel Valley home.

Officer Shaun Diamond, 45, was shot in the back of the head as he helped serve a warrant at a home in the 100 block of San Marino Drive in San Gabriel, the Pomona Police Department said. Diamond was one of several officers trying to open the outer door of the home when “the interior door opened and he was met with gunfire.”

Sheriff’s Lt. Eddie Hernandez said one shot was fired from a shotgun, apparently striking Diamond in the back of the head, even though the officer was wearing a Kevlar helmet.

Preliminary information indicated that officers did not return gunfire, Nishida said.

“The officers at this point didn’t have a clear shot at the suspect,” he said. “The suspect, we’re being told, laid on the ground and put the firearm to his side. Also the (suspect’s) father was in the way and at that point it became a rescue operation to get the officer some medical attention. The suspect was taken into custody without incident.”

The suspect was identified as David Martinez, 36, of San Gabriel.

Martinez’s father was also injured when the shot was fired. Hernandez said the man was struck in the left arm above the elbow.

Martinez was booked on suspicion of attempted murder on a peace officer and was being held on a $4 million bail. Sheriff’s officials said Martinez has a criminal history that includes assault with a deadly weapon and domestic violence.

Diamond began his law enforcement career with the Los Angeles Police Department, then joined the Pomona department in 2006, Pomona police Chief Paul Capraro said. Diamond joined the SWAT team in 2008.

“He’s a top notch guy — a great sense of humor and just a wonderful human being,” Lt. Mike Keltner said Diamond.

The shooting occurred while officers were serving a search warrant that stemmed from a larger investigation involving outlawed motorcycle gangs, according to police.

“Motorcycle gangs, just like typical other gangs, are involved with drugs, laundering money, weapons, violence — anything that enhances their gangs,” Keltner said.

Numerous other warrants related to that investigation were also served throughout the LA area.

A command post was set up in the area of Las Tunas and San Marino avenues in San Gabriel.