The manhunt for two escaped murderers took authorities to southwestern New York on Saturday.
State Police said they were following leads in Allegany County in the search for Richard Matt, 48, and David Sweat, 35.
A law enforcement source briefed on the prisoner investigation told CNN there was a credible sighting of the escapees near the town of Friendship, just north of the Pennsylvania border.
State police, however, called it an “unconfirmed sighting.”
The sheriff’s office said someone called in a tip that led authorities to tracks that police were following to see whether they led to the two convicted killers.
Heavily armed police and law enforcement agents were walking along a railroad near Friendship, another source told CNN. State police said two men were spotted near the rail line earlier.
CNN affiliate WIVB in Buffalo sent one of its reporters to Friendship, where she was asked to leave the search area because state police said it was a “hot spot.”
Emergency services radio traffic monitored by CNN indicated police were moving large numbers of officers into the area. Responding officers were asked at one point to maintain radio silence.
Police were pursuing other possible sightings of the two men, who broke out from Clinton Correctional Facility in upstate New York.
Possible sightings happened last weekend in Steuben County, about 45 miles east of Friendship, state police said in a news release Friday evening.
“Witnesses spotted two men on June 13 walking near the Gang Mills railyard on Rita’s Way in the town of Erwin,” police said. “The next day, two men with the same description were spotted walking along County Route 115 in the town of Lindley, heading toward the Pennsylvania border.”
The unconfirmed sightings came from two separate individuals, police spokesman Beau Duffy told CNN on Saturday.
The sightings were not reported to New York State Police until Tuesday. State police sent investigators at that time to the areas to conduct interviews, according to Duffy.
Investigators have collected “inconclusive” surveillance camera video that is being sent for further analysis.
On Saturday, police urged people living in the Allegany County area along the New York-Pennsylvania border to be on alert for Matt and Sweat, both of whom have killed in the past.
“Do not approach, as both are considered to be very dangerous,” officials warned.
In another development, the state corrections department said a corrections officer was placed on administrative leave as part of the investigation into the escape. The officer’s name was not released.
The district attorney declined to comment but said the corrections officer was male.
Most wanted list
The U.S. Marshals Service has added Matt and Sweat to its list of the 15 most wanted fugitives and offered a $50,000 reward for information leading to their capture.
The list “is reserved for the worst of the worst,” said U.S. Marshals Service Director Stacia Hylton. “There is no question David Sweat and Richard Matt fall into this category.”
Authorities warned Friday that the search could take some time as the massive manhunt enters another week.
“We’re configured now for a rapid response,” New York State Police Maj. Charles Guess said at a news conference.
“We’d like nothing more than to place them into custody today. … However, we’re also geared for the long haul, the state police and our partners. … We’re no strangers to lengthy months and yearlong investigation.”
As many as 800 law enforcement officers have participated in the manhunt, which has cleared nearly 200 abandoned buildings, hundreds of occupied homes and more than 600 miles of rural trails, officials said.
“We’re not going anywhere,” Guess said. “Our plan is to pursue these men relentlessly until they are in custody.”
Back at the prison, the breached prison cell walls, steam tunnels and pipes and other areas involved in the escape have been repaired, and a lockdown has been lifted, according to Daniel Martuscello, a deputy commissioner of the state corrections department.
State police have asked hunters and homeowners with surveillance cameras to check their footage all the way back to June 6, the day of the prison break, for any unusual activity.
The search has reached all the way to the borders Canada and Mexico, where wanted posters of the escaped killers are being handed out.
Questions over Joyce Mitchell
New details are emerging about the relationships between the convicts and prison tailor shop instructor Joyce Mitchell, who has been charged for aiding in escape.
Her husband, also a prison employee, feels betrayed by what happened, his attorney says.
Joyce Mitchell, 51, is behind bars, accused of helping the inmates break free and sneaking hacksaw blades, chisels, drill bits, a punch and other contraband into the convicts’ hands before they broke out.
Authorities have said Matt had a sexual relationship with Mitchell.
No court date has been set for Mitchell, who has pleaded not guilty to the two charges brought against her and has been talking to authorities. If convicted, Mitchell could face up to eight years behind bars.
Mitchell’s husband, Lyle, also worked in the prison’s tailoring block.
But the prosecutor said Wednesday that Lyle Mitchell didn’t know about the prisoners’ escape plan before it happened and wasn’t aware of his wife’s relationships with the inmates.
CNN’s Shimon Prokupecz, Deborah Feyerick, Linh Tran, Joe Sutton, Jethro Mullen, Eliott C. McLaughlin, Susanna Capelouto, Anne Woolsey, Alexandra Field, Randi Kaye, Danelle Garcia and Jason Carroll contributed to this report.