(NewsNation) — Investigators are searching a property in South Carolina belonging to Rex Heuermann and looking into unsolved cases in Las Vegas as the investigation into the prime suspect in the Gilgo Beach murders expands.

Heuermann was arrested last week in connection with the deaths of at least three women found along Gilgo Beach in Long Island, New York.

The suspected serial killer is currently in an isolated cell on suicide watch. Police tell NewsNation he rests in bed and doesn’t make a fuss. Police also added he has a television but doesn’t watch it or ask to see a newspaper.

“It just seems like at this point, he is in his cell, by himself, reflecting or sleeping, until his court date on August 1,” said Suffolk County Sheriff Dr. Errol Toulon.

Investigators began wrapping up the search of Heuermann’s Long Island house Wednesday. The search revealed portraits of battered women and life-sized dolls kept in glass boxes.

In nearby Amityville, New York, detectives cleaned out a storage space tied to Heuermann. Police were seen carrying large boxes of confiscated goods into their evidence trucks.

Five states and more than 700 miles from Heuermann’s New York home, the Chester County sheriff’s office is searching his South Carolina property. The sheriff’s office says it is assisting in collecting information that could link Heuermann to other violent crimes around the country.

“The Chester County Sheriff’s Office has and will continue to work closely with the Federal Bureau of Investigation (FBI) and Suffolk County law enforcement authorities during this very important and arduous investigation,” the Chester County Sheriff’s Office said in a Facebook post.

On Tuesday morning, New York State Police arrived at the South Carolina home and hauled away what appears to be a Chevrolet truck.

A witness had spotted a Chevy Avalanche truck around the time one of the victims went missing, a clue that ultimately led them to Heuermann. Property records show he owns nearly 22 acres of land valued at more than $155,000 in Chester County. Heuermann’s brother reportedly lives nearby.

Tax records show Heuermann also owns a condo near Las Vegas, Nevada. The Las Vegas Metro Police Department told NewsNation it is reviewing all of its cold cases to see if there is any connection to Heuermann.

According to Suffolk County Police Commissioner Rodney Harrison, it is not outside the realm of possibility that Rex Heuermann could be linked to other violent crimes across the U.S.

“Any evidence, be it linked to the bodies that were discovered on Ocean Parkway or anywhere across the country. We want to try to link it to Mr. Heuermann,” Harrison said. “We’re concerned. We don’t know if these are the only ones that he killed.”

NewsNation spoke with the sister-in-law of Heuermann about the killings. She said the news came as a shock to her family and that she’s learning about the case from NewsNation reporting.

Heuermann’s Long Island neighbor shared a number of uncomfortable encounters he and his wife had with the suspected serial killer, accusing him of peeking over their fence as his wife sunbathed.

“At first I thought, he was trying to be neighborly. And then after it kept happening every time she went out there, finally it started to creep her out. And she felt uncomfortable and I had to do something about it,” Etienne Devilliers, Heuermann’s next-door neighbor said.