The Grand County, Utah, Sheriff's Office released on Monday a 911 recording from August in which a caller claimed he witnessed Brian Laundrie allegedly "slapping" Gabby Petito and chasing her up and down a sidewalk hitting her.

In the recording of the 911 call from Aug. 12, the caller, whose name was not released, claimed he saw an apparent domestic dispute unfold on Main Street in Moab between a young couple driving a white van with Florida license plates.

"We drove by, and the gentleman was slapping the girl," the caller told a 911 dispatcher. "And then we stopped. They ran up and down the sidewalk. He proceeded to hit her, hopped in the car and drove off."

Moab Police Department Chief Bret Edge said last week that his officers responded to the incident, located the van and pulled the couple over. Moab police released body camera footage of the traffic stop and wrote in a report that the couple, identified as Laundrie and Petito, admitted to arguing and that Petito had slapped Laundrie.

The couple also stated to police that Laundrie did not hit Petito, according to the report.

After speaking to Petito and Laundrie separately, the police allowed the couple to go on their way. Edge said "insufficient evidence existed to justify criminal charges."

A Ford Mustang convertible authorities believe Brian Laundrie used to purportedly drive himself to the Carlton Reserve near North Port, Florida, was parked in the driveway of his family's home when FBI agents served a search warrant there on Monday.

Laundrie's parents told authorities he went to the nearly 25,000-acre preserve on Tuesday, which is the last time they claim they saw him, according to the family's attorney.

Steven Bertolino, the Laundrie family attorney, told ABC News that the family picked up the car on Thursday morning from the reserve after going out on Wednesday to look for Laundrie.

Laundrie left his family's home on Tuesday morning with a backpack, Bertolino said. He said that when family members went to the reserve to look for him, they spotted a note left on the car from the North Port Police Department saying it needed to be removed.

Bertolino said the family left the car overnight “so he [Laundrie] could drive back." When Laundrie didn’t come home Thursday morning, the family went back to retrieve the car, the attorney said.

The family called the police on Friday to file a missing person report, authorities said.

Police and FBI agents descended on the home of Laundrie's parents in North Port, Florida, to serve a search warrant Monday morning, authorities said.

Officers escorted the parents from the home to an FBI vehicle, an ABC News photographer at the scene observed. They were later allowed back into their home.

The FBI field office in Tampa tweeted that agents were at the home to serve a search warrant.

The North Port, Florida, Police Department said on Monday that a search for Laundrie in the vast Carlton Reserve near North Port has been "exhausted."

Josh Taylor, a spokesperson for the North Port Police Department, told ABC News that the two-day search of the nearly 25,000-acre swampland preserve turned up no sign of Laundrie.

Taylor said search dogs did not pick up the scent of Laundrie while searching the preserve, which authorities described as alligator infested.

"At this time, we currently believe we have exhausted all avenues in searching of the grounds there," Taylor said in a statement. "Law enforcement agencies continue to search for Brian Laundrie."

Police returned on Tuesday morning to the vast Carlton Reserve near North Port, Florida, to resume their search for Brian Laundrie a day after they said they had "exhausted all avenues in searching the grounds."

A North Port Police Department spokesman released a statement saying police, FBI, the Florida Fish and Wildlife Conservation Commission and other law enforcement agencies resumed the search for Laundrie on the Venice, Florida, side of the roughly 25,000-acre preserve.

Laundrie's parents told police their son said he was going to the preserve on Sept. 14 and that was the last time they heard from him.

Police spent most of Saturday and Sunday searching the preserve, entering from the North Port side. Josh Taylor, the North Port police spokesperson, said on Monday that the initial search of the preserve turned up no clues of Laundrie's whereabouts there and that bloodhounds and K-9 units did not pick up Laundrie's scent.

"Please be aware, the Carlton Reserve is a vast and unforgiving location at times. It is currently waste deep in water in many areas. This is dangerous work for the search crews as they are wading through gator and snake-infested swamps and flooded hiking and biking trails," Taylor said in the statement released on Tuesday.