An Orange County, Florida, motorcycle deputy died Monday after he was struck and killed by a van while working a perimeter in the search for the man suspected of shooting and killing an Orlando police officer, according to the Florida Highway Patrol.

The crash happened on Pine Hills Road and Balboa Drive at about 9:43 a.m.

"In my 36-year career, this is probably one of the toughest days in my career," Orange County Sheriff Jerry Demings said at a news conference.

The deputy, who has not been identified, was struck while traveling south on Pine Hills Road. He did not have his lights or sirens on, but Demings said witnesses told authorities the deputy had a green light.

A van traveling north on Pine Hills Road made a left turn into the direct path of the motorcycle, which struck the right side of the van, authorities said.

A witness told WFTV he went to help the officer after finding the officer on the ground.

"When I went up to him, he wasn't breathing," the man said. "He was down, nobody was helping him, so I ran to him to see what I could do to help."

He followed the instructions of a nurse, who also came to the deputy's aid.

"I was holding his hand and trying to keep him alive, keep him awake – tapping on his arm, taking off his clothes so he could breathe easier," the man said.

"He was in and out. He didn’t say anything. He was actually mostly unconscious and then he came back and squeezed my hand and his hand – his arm was going cold. But he started breathing again, it seemed like he was going to make it. I thought he was going to make it."

The deputy was taken to Orlando Regional Medical Center, where he later died from his injuries.

"He was the best, he really was," Florida Highway Patrol Sgt. Kim Montes said in an emotional statement. "And I know people say that all the time but everybody knows this guy -- just a loving, wonderful human being."

The driver of the van was not hurt.

Authorities said Markeith Loyd, 41, is accused of firing multiple shots at Orlando police Sgt. Debra Clayton Monday morning, killing her. Loyd remains at large.