Investigators believe they have linked the 60-year-old man to the deaths of two more women.
Heuermann has already pleaded not guilty in the killings of four other women.
This comes after recent searches in the woods in Manorville and the North Sea, and in Heuermann's Massapequa Park home.
Evidence is believed to have been recovered from the basement, resulting in the new expected charges.
There has been a sweeping expansion of the investigation into Heuermann, a former New York City architect, following his arrest last summer.
At least 11 sets of human remains have been found in Long Island's Suffolk County, including the four women Heuermann is accused of killing: Megan Waterman, Melissa Barthelemy, Amber Costello, and Maureen Brainard-Barnes.
Their remains were found near Gilgo Beach along Ocean Parkway.
"These are long day searches with a lot of resources and this is the fruition of those searches," said Robert Boyce, ABC News Contributor and Former NYPD Chief of Detectives. "So now all of a sudden we'll have more information on Thursday, and hopefully some family has a little more justice than they had a few days ago."
Heuermann has pleaded not guilty to all murder charges and is being held without bail.
Thursday's proceedings will get underway at 9:30 a.m. in Riverhead.
Suffolk County District Attorney Ray Tierney is expected to discuss the new charges further following court.
"There were a number of investigative steps that were taken. Thursday you'll see the fruits of that investigation," Suffolk County District Attorney Ray Tierney said.
ALSO READ: Gilgo Beach murders: Complete timeline of events leading up to Rex Heuermann's arrest
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