PAGELAND, South Carolina (Reuters) - As sheriff’s investigators threaded past the battered cars, cast-off tires and rusted farm equipment cluttering Brent Nicholson’s front yard, there was no hint of the sinister stockpile hidden behind his windowless front door.

Inside, the guns were everywhere: rifles and shotguns piled in the living room, halls and bedrooms; handguns littering tables and countertops. Outside, when they rolled up the door on the pre-fab metal garage, more arms spilled out at their feet.

“This has completely changed our definition of an ass-load of guns,” said Chesterfield County Sheriff Jay Brooks. Six weeks after the discovery, officers are still cataloging the weapons, many of which have proved stolen, and the final tally is expected to be close to 5,000. “I don’t know if there’s ever been (a seizure) this big anywhere before,” Brooks says.

The question of how one man amassed such a stockpile of guns arises just as there is renewed American soul-searching over the widespread availability of firearms in the wake of a series of mass shootings.

Even in a country where more people own more guns than anywhere else in the world, Nicholson’s cache is extraordinary. The U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives doesn’t rank gun seizures by size, but a spokesman says Nicholson’s hoard probably is among the largest ever.

Yet when and why Nicholson set out to amass such an arsenal remains a mystery. Investigators are trying to determine whether he was simply a gun-obsessed hoarder or a supply valve in the “Iron Pipeline” of illegal firearms flowing from the south to New Jersey, New York and other northern states.

Nicholson, jailed on multiple charges of possessing stolen property, has not entered a plea or retained an attorney, court records show. His wife, Sharon Nicholson, facing similar charges and free on bond, declined to discuss specifics of the case but stressed in a brief interview that her husband buys his guns legally.

The Nicholson case raises issues that are fueling an increasingly heated national dialogue on the modern-day implications of Americans’ constitutional right to bear arms, which puts no limits on the number of weapons citizens can own. The uncertainty over how he got his guns – and what he was doing with them – underscores disputes over private gun sales, gun registration and what the government should know about who owns firearms and how they change hands.

Now, the spate of mass shootings, capped by Wednesday’s spree by a heavily armed couple who killed 14 at an office holiday party in San Bernardino, California, has pushed those issues to the fore in the presidential campaign. The massacre, which follows an attack that killed three last Friday at a Colorado Planned Parenthood clinic and an Oct. 1 rampage by a gunman who killed 10 at an Oregon college, prompted Hillary Clinton, leading candidate for the Democratic nomination, to renew her call to “stop gun violence now” with new firearm purchase restrictions. Conversely, those who top the polls for the Republican nomination, Donald Trump and Ben Carson, insist the answer to gun violence is to empower citizens to thwart such attacks by making it easier, not harder, to buy and carry weapons.

It wasn’t hard for Nicholson.

Slideshow ( 6 images )

A FAMILY TRADITION

Just about everyone knows the Nicholsons in this struggling town of 2,700, where the textile industry’s regional decline has helped strand median household income at $26,500 a year, half the U.S. average, and burglary rates run well over national norms. Firearms are a cultural staple – hunting clubs and cabins dot the county – and people say Nicholson’s penchant for guns was a family affair.

“Everybody knew he’d buy guns; his father bought ‘em, his grandfather bought ‘em,” says Al Padgett, 68, who keeps a booth at a local flea market and says he’s known the family all his life. “He collected ‘em, hoarded ‘em, but I never knew him to sell a gun. Not one. He did everyone a favor keeping ‘em off the street.”

Brooks sees things differently. Nicholson had piles of allegedly stolen goods, including a zoo’s worth of taxidermy trophies, Brooks says, but his preference was guns and he provided a ready market for burglars who grabbed them from cabins and hunting camps. The sheriff still hasn’t determined precisely how many guns in Nicholson’s cache were stolen, noting that hundreds have had their serial numbers removed so they can’t be traced.

“Getting him locked up dries up the outlet for this stolen merchandise,” Brooks says.

Brooks suspects Nicholson may have been selling some of the guns. He had relatively few handguns – maybe a half-dozen large buckets full – and “that makes us believe he had a market for those and was moving them north,” Brooks says, noting that the matter remains under investigation.

South Carolina is a common starting point for firearms moving up the Iron Pipeline, a route for many of the 230,000 or so guns stolen nationwide each year. The South has more gun thefts than any other region, federal data show, and police in New York and other northern cities say they regularly tie those guns to crimes, though there is no data on how often.

Stemming the flow is a challenge, law enforcement officials say, because it’s not organized groups moving truckloads of weapons; it’s a loose web of individuals who sell guns more as an occasional sideline than a full-time endeavor.

A SHADOWY PATH

On Oct. 21, a sheriff’s deputy just over the state line in Union County, North Carolina, pulled Nicholson over for running a stop sign. Nicholson’s pick-up had bogus license plates – and the deputy noticed rifle barrels poking up from behind the seat when he approached the vehicle.

A search turned up 20 rifles, nine handguns and nearly 200 hydrocodone pills, arrest records show, and several of the guns were stolen. Nicholson was arrested for possessing stolen weapons, trafficking in opiates and vehicular violations.

Slideshow ( 6 images )

Nicholson was still jailed 48 hours later when a deputy in Pageland stopped by his house with a subpoena in a family court matter. The deputy spotted equipment in the yard that had been reported stolen, and investigators returned with a search warrant. They’d spend the next six days removing guns, hundreds of cases of ammo, and other goods.

“He was going up to Union County to do something with those guns; we don’t know what,” Brooks says. “We’ve got information that he was moving some of these goods and … we’re looking at his activities to see if he was part of something more organized.”

Tracking Nicholson’s guns is a challenge because many states, including South Carolina, don’t regulate private gun purchases, which are unrestricted and require no background check. So person-to-person sales, including gun show transactions that don’t involve licensed dealers, are largely untraceable.

There also is no national gun registration mandate – only some state laws. So, unlike, say, cars, which can be tracked through registrations, guns often have no traceable ownership trail beyond their last sale by a licensed dealer.

It’s an issue that also is complicating efforts to trace the origin of the two assault-style rifles and two handguns used in Wednesday’s shooting spree in San Bernardino. The guns initially were bought legally: two by someone “associated with” the case and two by someone with no apparent link, according to ATF spokeswoman Meredith Davis. But it’s still not clear how those guns got to the shooters.

President Barack Obama and the major Democratic presidential candidates support background checks for private firearms sales; Leading Republican candidates generally oppose additional gun controls, echoing the National Rifle Association’s position that they’re unnecessary constraints on gun owners’ 2nd Amendment right to bear arms.

None of the proposals being floated on either side of the political spectrum would limit the number of guns someone can own.

A HUNT FOR OWNERS

So far, investigators have identified owners of just a fraction of Nicholson’s guns. Even those that still have serial numbers can be traced only to the last time they passed through a licensed dealer. And since there’s no requirement that gun owners record those numbers, many who believe their guns were stolen and sold to Nicholson are unable to prove the weapons belong to them.

Sharon Nicholson, 52, said in a brief interview at the family’s liquor store that her husband typically bought his guns at stores, but Brooks says investigators have found no records of any purchases he may have made from licensed dealers.

Ultimately, the courts will decide what happens to Nicholson’s guns. Brooks suspects many will be destroyed, particularly those with no serial numbers, because their rightful owners can’t be identified.

Some locals scratch their heads over that possibility, arguing that it’s a waste of good weaponry. Nicholson may not have known if he was buying weapons that prove to be stolen, some say, and he should be allowed to keep any that do not.

“It doesn’t make sense,” says Otis Burch, 85, another local who knows the Nicholsons. “He’s a good man – he wasn’t selling those guns.

“I asked him just about a month ago if he’d sell me a deer rifle,” Burch adds, “and he said he didn’t have any.”