(NewsNation) — Two sex workers have claimed that accused Gilgo Beach serial killer Rex Heuermann was “violent” and “aggressive” when they encountered him, according to police.

Suffolk County Sheriff Errol D. Toulon, Jr. told NewsNation’s “Banfield” on Tuesday that several sex workers were interviewed by the county’s anti-human trafficking unit at the Riverhead and Yaphank jails late last month.

Toulon said the department is still working to verify the interviews before releasing more information.

“We’re looking at dates, times, locations just to verify this story,” Toulon said.

Heuermann, 59, has been charged in connection with the deaths of three women whose bodies were found in 2010 and 2011 along a stretch of highway on Long Island’s Gilgo Beach. He’s the lead suspect in a fourth death. All of the victims were sex workers and were found wrapped in burlap sacks.

“As the task force progresses, we’re trying to make sure that we have concrete evidence,” Toulon said. “We want to be very clear and concrete when we present this evidence to the courts that we have the correct person.”

Court documents outlining the case allege Heuermann set up an account on Tinder under an alias and used a burner phone to contact his victims.

Prosecutors said an email account associated with a burner phone connected to Heuermann was used to search for sex workers, torture-related pornography and child pornography.

The account was also allegedly used to search for information about serial killers and the investigations into the deaths of women whose bodies were found in the Gilgo Beach area, according to court documents.

Erin Pflaumer contributed to this report,