(CNN) —  Probes into Gilgo Beach serial killings suspect Rex Heuermann now reach across the country as investigators are examining his connections to Las Vegas and South Carolina, where the suspect has owned property.

Police in Las Vegas are sifting through their roster of unsolved cases for any sign Heuermann may have been involved, a spokesperson for the Las Vegas Metropolitan Police Department confirmed in a statement.

Though Heuermann lived on Long Island, New York, he and his wife had purchased two timeshare condos in Las Vegas between 2003 and 2005, according to property records obtained by CNN. The couple has since sold the first property, the records show, and it is unclear whether they still own the second.

The 59-year-old architect and father of two was arrested last week in New York City and charged with the murders of three of the “Gilgo Four,” a group of four women whose remains were found along a short stretch of Long Island’s Gilgo Beach in 2010.

Heuermann has pleaded not guilty in the murders of Melissa Barthelemy, Megan Waterman and Amber Costello. He remains the prime suspect in the killing of the fourth victim, Maureen Brainard-Barnes, but has yet to be charged in the case.

As authorities scour Heuermann’s home, office and storage unit, they are operating under the assumption that the suspect may have continued his alleged killing spree after the bodies of the Gilgo Four were discovered, a source familiar with the case told CNN.

Who is Rex Heuermann? What we know about the Gilgo Beach murders suspect

The sheriff’s office in northern South Carolina’s Chester County, where tax records show Heuermann owns four large parcels of land, says it has been gathering evidence for the Gilgo Beach investigative task force since before the suspect’s arrest.

Authorities were seen towing a truck belonging to Heuermann’s brother late last week, according to neighbor Steve Caston, who lives down a gravel road from the brother and adjacent to land owned by Heuermann. Caston described deputies lined up with “assault rifles” and “the whole nine yards,” as the vehicle was being seized but he said the scene was “fairly quiet” with “no screaming, no yelling.”

A Chevy Avalanche truck seized from the property is being combed for evidence, sources told CNN.

FBI investigators were also seen talking to neighbors in the rural South Carolina neighborhood on Tuesday. As a CNN crew was speaking to Caston at his home, he was approached by two men in plainclothes who identified themselves as FBI agents and asked the neighbor to contact them later that day.

The multi-agency cold case task force is “actively investigating” whether Heuermann may have had more alleged victims as they pore over a flood of tips and new evidence, Suffolk County Deputy Police Commissioner Anthony Carter said Monday.

Heuermann’s family was stunned when authorities informed them of the harrowing allegations against him, Police Commissioner Rodney Harrison said Monday. “They were disgusted. They were embarrassed,” he said.

“So, if you ask me, I don’t believe they knew about this double life that Heuermann was living.”

Long-dormant investigation gets flood of evidence

As investigators pore over Heuermann’s home, they are primarily focused on gathering forensic evidence but are also searching for things that could be souvenirs kept from the killings, including items that are hidden or stashed where family members wouldn’t find them, according to a source with knowledge of the case.

Any found items will then need to be shown to victims’ family and friends, a process that could take some time, the source said.

The search of the home has so far revealed a cache of between 200 and 300 firearms hoarded in a vault behind a locked metal door – far more than the 92 firearms authorities knew Heuermann had registered in the state, the source said.

Prosecutors have detailed a trove of evidence used to connect Heuermann to at least three of the Gilgo Four killings, including credit card bills, cell phone data and DNA evidence.

The four women’s bodies were among a string of 11 sets of human remains found scattered along Long Island’s South Shore between 2010 and 2011, sparking what police have called “one of the most consequential homicide investigations” in the island’s history.

Striking similarities soon emerged between the cases of the four women. Each of the remains had been bound in camouflaged burlap and hidden along the same quarter-mile stretch of Ocean Parkway, authorities said. The women – who disappeared between 2007 and 2010 – all worked as escorts and advertised their services on Craigslist, according to police.

But it took more than a decade for investigators to match DNA from a male hair found on the burlap wrapping to a sample of Heuermann’s DNA surreptitiously collected from a pizza crust the suspect threw away after the cases were reopened, according to the Suffolk County District Attorney Ray Tierney.

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Authorities have said the killer used burner phones to contact the victims and investigators were able to use cell phone and credit card records to identify several instances when Heuermann was in the general location when the phones were used to call the victims, according to a bail application.

Though prosecutors have said Heuermann is the prime suspect in the fourth killing of Brainard-Barnes, police commissioner Harrison said Monday that bringing a charge in that case may “take a little time.” A hair follicle investigators have as evidence needs to undergo DNA testing, but has been damaged, he said.

Meantime, he said, “It’s a very good thing that we got this animal off the streets.”