Authorities plan to offer a reward in hopes of flushing out two alleged cop killers who so far have eluded detection since May 29 despite one of the biggest manhunts ever in the Four Corners area.

Even though commanders have scaled back the search for Alan "Monte" Pilon, 30, of Dove Creek and Jason Wayne McVean, 26, of Durango, four Colorado National Guard helicopters were in the air and up to 80 officers on the ground Monday searching the southwest corner of Colorado.That was a sharp reduction from the 500 men in the field at the peak of the manhunt in the desert canyonlands along the Colorado-Utah border.

Cortez Police Chief Ray Lane told reporters Monday night: "I'm sorry to say . . . that not a lot of positive things happened."

Lane said investigators were going back and requestioning witnesses to see if they had missed anything, and teams were going back over potential hiding places.

The Hovenweep National Monument is one of those. The National Park Service ordered it temporarily closed Monday afternoon. Lane said that was just a precaution and not an indication of any tracks or traces of the men.

Three men fired on a National Park Service employee in Hovenweep on May 29 after fatally shooting Cortez policeman Dale Claxton and wounding two Montezuma County sheriff's deputies.

The third alleged member of the group, Robert Matthew Mason, 26, of Durango, apparently split from the group and hiked more than 40 miles through the rugged canyon country to Bluff, Utah, where he wounded a San Juan County sheriff's deputy after being spotted. Mason shot himself to death minutes later.

The shooting in Utah shifted the manhunt there for several days, and at one point the town of Bluff was evacuated and more than 500 service support staff from 51 state, federal and local agencies were involved.

Lane said that not only were officers interviewing witnesses again, they also met among themselves Monday afternoon to discuss what happened and how to deal with it. He said, "It was a very emotional session."

City Manager Bill Ray said officers have worked hundreds of hours of overtime since then and are donating their extra pay to the Claxton family.

The manhunt began in Cortez on May 29 after the three men allegedly killed Claxton, who pulled them over in a stolen water truck.