Another possible sighting of the suspect in the deadly ambush of a Pennsylvania state trooper has been reported, as the manhunt for the alleged killer now nears its 50th day.

Hundreds of state troopers converged on the Buck Hill Inn in the Pocono Mountains late Friday in search of suspected cop-killer Eric Frein, who has eluded a massive manhunt for the past month and a half. The search — now in its 47th day — included dozens of vehicles and a helium balloon, the (Scranton) Times-Tribune reports.

“They had a helicopter flying so low you could see the color of the bottom of their boots,” witness Dave Kreckman told the newspaper.

The unsuccessful search follows another possible sighting of the 31-year-old fugitive on Tuesday in Barrett Township, which surrounds the community of Canadensis, where Frein lived. Trooper Connie Devens declined further comment on the report.

Frein allegedly opened fire outside the Blooming Grove state police barracks on Sept. 12, killing Trooper Bryon Dickson, 38, and seriously wounding Trooper Alex Douglass, 31. A pair of possible sightings over a four-day period last week prompted closure of nearby schools.

Pennsylvania State Police had received assistance from authorities in Ohio in the hunt for Frein in the form of an unmanned balloon to serve as an eye in the sky. Detectives hoped the so-called "blimp in a box" on loan from Ohio’s Department of Transportation could help them get locate the self-styled survivalist, but Pennsylvania authorities returned the device after thick tree canopy rendered it unhelpful, Pennsylvania State Police Trooper Thomas Kelly said Monday.

The 15-foot balloon, which had previously flown above prisons in Ohio, was briefly tethered nearly 500 feet above the Pocono Mountain region where Frein is believed to be hiding. 

Dan Erdberg, the chief operating officer of Drone Aviation, said the blimp’s camera can spot people as far as 3 miles away and groups or vehicles as far as 5 miles away. Inflating the blimp with helium costly $1,000, he said.

State, local and federal authorities reportedly believe they have Frein contained in a 5-mile radius. Earlier this month, Pennsylvania State Police revealed information from a journal found in the woods in which Frein allegedly described shooting the state troopers. They also detailed campsites where Frein is believed to have hid, cooking over small fires even as hundreds of heavily armed police hunted him. Police have found pipe bomb booby traps and a gun resting against a tree, but have only had a handful of unconfirmed sightings of Frein.

"Got a shot around 11 p.m. and took it," Frein wrote on papers found by police. "He [Dickson] dropped. I was surprised at how quick."