(CNN) -- Law enforcement authorities combed rugged terrain south of the Utah-Arizona border Friday for the suspect in Thursday's fatal shooting of a Utah sheriff's deputy.
"This morning, we had law enforcement officers in the field in a variety of terrains and settings," Jim Driscoll, chief deputy for the Coconino County Sheriff's Department told reporters in Fredonia, Arizona, three miles from where the shooting occurred and just south of the Utah border.
In all, 121 law enforcement personnel from 21 agencies were involved in the manhunt, Driscoll said.
The incident began Wednesday night, when Scott Curley, 23, "apparently assaulted a janitor at the local high school," said Alan Alldredge, emergency services director for the Kane County Sheriff's Department in Kanab, Utah.
Efforts to find Curley Wednesday night proved fruitless, but on Thursday officers from Kanab spotted him and began a pursuit on foot, Alldredge said. They called in their counterparts from nearby Fredonia to join in, he said.
"Apparently, with his knowledge of the area, it's possible he knew of a spot where he could ambush the officers," Alldredge said. "He was laying in wait underneath a tree. When these officers came up over the rise, he had his sights on them and fired upon them."
A high-power rifle shot fatally struck Kane County Deputy Brian Harris, a 13-year veteran, and Curley escaped.
Helicopters, SWAT teams and dog teams were dispatched to the area to contain Curley overnight.
But law enforcement officials began to question whether they had succeeded when, at 7:30 a.m. Friday, a resident east of Kanab and north of Fredonia reported to law enforcement officials that she had seen a man matching Curley's description walking near her house.
"He had something strapped to his back that was possibly a firearm; he was dressed in a brown shirt and jeans and a brown cap, which is consistent with the information we had as to how Mr. Curley was dressed yesterday after the shooting," Driscoll said.
Meanwhile, other possible sightings of Curley have been reported to authorities, all of which are being followed up, he said.
"We will attempt to apprehend Mr. Curley alive, but if Mr. Curley takes that option away from us, we will do what we need to do," Driscoll added.
He described Curley, who knows the area well, as "very mobile, very agile, and able to cover pretty good distances on foot."
The situation will become more difficult after sunset, he predicted. "Once we have darkness, it changes the whole game plan," he said. "If this was, in fact, him this morning, he was able to move around more last night. It creates more difficult situations for us."
A warrant was being sought for a search of Curley's residence, and authorities were "trying to find out as much as we can about him," Driscoll said.
"We feel that he is in this area," he said, referring to the region around Kanab and Fredonia -- about a 12- to 18-square-mile area.
The weapon used in the killing was obtained through a burglary of the home of a friend of Curley, Driscoll said. "He had been shown the gun by a friend at one point," he said. Though at the time Curley showed little interest in it, "he definitely knew it was there."
Asked what message he would send to Curley, Driscoll said, "I'd say, 'Mr. Curley, it's time to do the right thing and contact local law enforcement and give yourself up. Enough people have been hurt and it's time.'"
Curley is described as a Native American, 5-foot-7, 170 pounds with brown hair and brown eyes.