After two false alarms Monday, hundreds of law enforcement officials are still involved in an “intense manhunt” for the suspect accused of fatally shooting five of his neighbors in Cleveland, Texas.

Sheriff’s deputies, K9 units and air units searched an area where a person reported a possible sighting of 38-year-old Francisco Oropeza, but the Montgomery County Sheriff’s Office later said he was not among the people in the area. Another possible sighting prompted several schools to secure their campuses as local, state and federal officials searched the area and again did not find Oropeza, the sheriff’s office said.

Although more than 250 officers from over a dozen agencies are searching for Oropeza and $80,000 has been offered for information on his whereabouts, investigators have “zero leads,” James Smith, the FBI special agent in charge, told reporters Sunday. 

Law enforcement experts told USA TODAY in addition to scouring the area, investigators are likely trying to find Oropeza by digging into his past, interviewing people close to him and sorting through any tips from the public.

“This person’s off the grid, they’ve gone dark, which is expected,” said Lenny DePaul, the former chief inspector and commander of the U.S. Marshals’ New York/New Jersey Regional Fugitive Task Force. “Right now, you got an intense manhunt going on, but there’s also a fugitive investigation going on behind the scenes.”

“They’re chasing a ghost, unfortunately,” DePaul later added.

Ground search is ‘very much a necessity’

The investigation began after Oropeza allegedly opened fire with an AR-15-style rifle just before midnight Friday. Before the shooting, Wilson Garcia said he asked his neighbor to stop shooting his gun because Garcia’s 1-month-old son was sleeping and the family called police five times, according to the Associated Press.

Smith said officials believe Oropeza, who is considered armed and dangerous, fled the area on foot, but they don’t know for sure. 

Police were able to identify Oropeza based on a Mexican identity card and doorbell camera footage, San Jacinto County Sheriff Greg Capers said. Law enforcement set up a perimeter and found clothes and a cell phone in the area around the home, which includes a dense forest, according to Capers.