Utah law-enforcement officers worked late into the night Saturday in southern Utah searching for three men who brutally killed a Colorado police officer Friday morning.

"We still haven't found anything yet," said San Juan County Deputy Sheriff Mike Harris. "Nothing new has happened."The manhunt for the men, considered to be armed and dangerous, has area residents on edge.

"We live on a ranch halfway between Blanding and where the men are," said Gary Guymon, owner of the Blanding Sunset Motel on the Utah side. "My daughter was worried about it last night, so we didn't go home. We stayed at the motel. Those guys are out there somewhere."

An FBI night search plane joined the manhunt Saturday night.

Cortez City Manager Bill Ray said the FBI plane would make its initial flight Saturday night.

"It's probably got some of the most sophisticated night tracking abilities available," Ray said from the Cortez police station.

The FBI search plane joined four Colorado National Guard Black Hawk helicopters equipped with both infrared heat-seeking devices and night vision capabilities that Colorado Gov. Roy Romer dispatched earlier Saturday.

The aircraft were supported by between 150 and 200 law enforcement personnel from four states on the ground, Ray said.

Three men killed Cortez police officer Dale Claxton, 45, after he pulled them over Friday about 9:45 a.m. The truck the men were in had been reported stolen out of La Planta County, east of Cortez.

Claxton was sitting in his patrol car when the gunmen jumped from the truck and opened fire with automatic weapons. Claxton was killed instantly.

"An event of this kind is unprecedented in this community," said Ray. "It's out of the scope of anybody's experience here. An officer was murdered while sitting in his car. He was assassinated. It's unbelievable to me."

Ray said the three gunmen were male Caucasians, wearing ski masks and dressed in camouflage suits.

"Nobody saw them very long. When they did, most of the time they were shooting. It may be in excess of 500 rounds they shot off at people yesterday (Friday)," Ray said.

Other officers set out in pursuit, chasing the truck northwest out of Cortez and exchanging shots along the way.

Two minutes after the initial shooting, the gunmen opened fire on two Montezuma County sheriff's deputies trying to pull them over. Jason Bishop was grazed on the head and Todd Martin was shot in the arm and knee. Bishop was released from Southwest Memorial Hospital in Cortez on Saturday.

Martin remained hospitalized. "The bullet that shot his left arm basically stripped away the flesh and muscle from elbow to shoulder," Ray said. "His kneecap was basically shattered by a bullet, but they will be able to put that back together."

Jim Fruit was working on the roof of a house in Cortez when he saw police cars chasing the truck.

"Then I heard gunshots," Fruit told the Associated Press. "The first ones were all the same caliber, and then I heard more shots from a larger caliber."

The gunmen eluded the deputies and headed northwest on U.S. 666. They managed to avoid several roadblocks along the route. They abandoned the flat-bed truck and stole a construction truck, police believe.

Authorities found the construction truck near the Hovenweep National Monument, just east of the Navajo Indian Reservation. Police found two automatic rifles in the vehicle, deputies said.

The shootings sparked an all-out manhunt in a rugged canyon area near the monument in San Juan County. Authorities believe the men are hiding there.

"There've been no sightings today" of the suspects, said Cortez Police Chief Roy Lane, but he said the search would continue around the clock "until we either know they're not in the area or we catch them."

Lane described the search area as rough and rocky canyon. It is usually dry but with spring runoff, water is plentiful now.

"There's just a whole lot of nothing out there. There's a lot of twisted canyon country, a thousand arroyos or pockets in side canyons" that are slowing the search, Lane said.

The fugitives had not been identified by Saturday evening, Lane said. The Colorado Bureau of Investigation was analyzing fingerprints from the stolen trucks and checking ownership of the two guns abandoned by the fugitives.

The loss of Claxton - a Cortez police officer for three years - has saddened the community and his fellow officers, Ray said. Claxton left behind a wife and two children.

"The community is deeply shocked and heartbroken over loss of Dale and the pain his family is feeling," Ray added. "It's a really tough situation."