Gardai are examining a gun found at the Trevor Deely search site to establish if it is connected to his disappearance.
The firearm was discovered in Chapelizod in Dublin yesterday after a tip-off that the remains of the 22-year-old could be buried there.
Gardaí have divided the search area into four zones and say the search of the derelict land may take several weeks.
Trevor was last seen in the city centre after his Christmas party almost 17 years ago.
A former detective has said ground penetrating radar is being used in the hunt for Trevor Deely's body.
Scrubland is being searched near the Liffey in Chapelizod in Dublin after a tip-off over the weekend.
Latest reports suggest Trevor Deely may have been shot by a known criminal and yesterday a gun was found at the search site.
The scene where gardaí are carrying out an excavation in the search for Trevor Deely pic.twitter.com/veHewUefOS
— Seán Defoe (@SeanDefoe) August 14, 2017
Former Detective Sergeant Alan Bailey has said the dig at the site is painstaking.
"It's almost three acres and it is overgrown," he said.
"In the past we've used ground penetrating radars, its a huge job, a finger tip search of ground.
"You've to clear it first (the ground), you're talking weeks and not days (for the search)."
Gardaí have reportedly found a gun during their excavation in Chapelizod as part of the Trevor Deely cold case.
The 22-year-old from Co Kildare disappeared after his office Christmas party in Dublin in 2000.
It is understood one line of inquiry for officers is whether Trevor was shot by a well known criminal before being buried in an area of scrubland near the banks of the Liffey.
The identity of the suspect came to detectives attention when new technology was able to enhance CCTV from the night Trevor Deely went missing.
Gardaí will have to establish whether the firearm has any connection to Trevor, whose body has never been found.