Both men charged in the bizarre Jefferson Parish sniper van case pleaded guilty Friday to federal firearms charges, an unexpected turn in a prosecution that carried overtones of organized crime.

In admitting guilt, the defendants, Dominick Gullo, 72, and Joseph F. Gagliano, 55, abandoned an alibi in which they professed ignorance about the contents of the van, which the authorities described as being specially outfitted for an assassin.

The vehicle, which attracted the attention of law enforcement last year after an automatic license reader flagged its stolen plate in Old Metairie, was equipped with sawed-off dining room chairs mounted in its interior, custom residential windows built into its side panels and a .22-caliber rifle with a scope and silencer secreted in its cargo area.

Gullo, who was driving the van the night in May when the authorities pulled it over, claimed he had bought the vehicle hours earlier from a stranger at a coffee shop on Metairie Road.

The men acknowledged Friday, however, that Gagliano, who was a passenger in the van when it was stopped, had ordered the custom residential windows — openings resembling gun ports — installed in the Ford E-250 in the weeks before the traffic stop.

“Investigating agents obtained documentation corroborating the work done at Gagliano’s discretion,” according to new court documents. That evidence had not initially been disclosed by the government and appeared to mark a turning point in the case.

Gullo and Gagliano, who had been scheduled to stand trial next month, each pleaded guilty to one count of possessing an unregistered silencer, a violation of the National Firearms Act. Gagliano, a convicted racketeer with reputed ties to organized crime, also pleaded guilty to being a felon in possession of a firearm.

Gagliano’s defense attorney, Pat Fanning, said he believes his client faces between two and three years behind bars. He faced a potentially longer sentence if he had stood trial and been convicted.

Gullo, too, could be facing a short jail term, despite his lack of criminal history, but his attorney declined to speculate after a hearing Friday in U.S. District Court.

“You’ll have to ask the judge that,” defense attorney Patrick Hand said outside the courtroom. “There’s no plea agreement.”

U.S. District Judge Eldon Fallon set sentencing for May 14 for both men.

The guilty pleas marked an about-face for both defendants, whose defense attorneys had assailed the government’s case as lacking substance and accused the authorities of conducting an illegal search of the van.

At about 11 p.m. May 7, the van passed a license plate-reading camera — a device that automatically scans the license plates of passing vehicles and alerts law enforcement to plates wanted for various offenses — near Orpheum Avenue and Metairie Road. The plate affixed to the van, according to a Jefferson Parish Sheriff’s Office report, had been swiped from a woman’s car in the parking lot of an unidentified hospital.

A deputy followed the van down East William David Parkway as Gullo pulled into his driveway. Gagliano got out of the passenger door but later denied even being in the vehicle. Gullo, meanwhile, “accessed the glove box for registration and insurance documentation for a brief time and then abandoned his efforts and admitted he did not possess registration and insurance paperwork for the van,” court records say.

Gullo fabricated a story about having bought the vehicle earlier in the day for $300 from a woman who walked into the coffee shop and asked whether anyone wanted to buy it. Gullo claimed he had taken the woman up on the deal, saying the woman promised to meet him the next day to give him more paperwork.

Authorities discovered the suspicious setup inside the van as they were preparing to tow it. They called a crime-scene technician to the scene and found the loaded rifle under a piece of folded carpet. “A further search of the van produced a silencer from a side door of the van as well as approximately eight feet of cannon fuse from the cargo area,” according to court documents.

The investigation, led by the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, found Gagliano “sought to have the Ford van repaired and modified, leading to the small residential widows being installed,” the documents say. Gagliano and Gullo both declined to comment on the van Friday, and it remains unclear what motive the men had for being inside — and lying about — the vehicle.

While many questions remain about the sniper van, the case harkened back to the city’s organized-crime days of yesteryear, which have become a distant memory as drug-dealing street gangs have become the top priorities for law enforcement. Gagliano’s father, Frank Gagliano Sr., had been the reputed underboss of the Marcello crime family before his 2006 death.

The younger Gagliano was sentenced to 42 months in federal prison in the 1990s after pleading guilty to a racketeering conspiracy involving video poker machines, an operation prosecutors said had used companies that served as Mafia fronts.

Follow Jim Mustian on Twitter,@JimMustian.