Suffolk County prosecutors want to collect more DNA evidence in their case against suspected Gilgo Beach serial killer Rex Heuermann — and are seeking a court order to get a cheek swab from the accused cold case murderer.

The DA’s office on Monday filed a request for a “buccal swab” from the hulking suspect, who is charged with the murder of three women whose bodies were found dumped on Gilgo Beach, Long Island, in December 2010, Newsday reported.

Prosecutors already have a DNA link to Heuermann from a hair found on the body of 22-year-old slay victim Megan Waterman — and are now looking for more evidence, the outlet said.

“If the defendant’s DNA from a buccal swab sample matches the mitochondrial DNA profile developed from Megan Waterman’s remains, there is scientific evidence of the defendant’s contact not only with Ms. Waterman and where her remains were discovered, but also with the burlap utilized to restrain and transport her human remains,” Assistant District Attorney Michelle Haddad wrote.

“Specifically, it is expected this information would provide further relevant evidence of the defendant’s identity as the perpetrator of these crimes,” the document said, Newsday said.

Heuermann, 59, was arrested on July 13 and charged with the murder of Waterman, Amber Lynn Costello and Melissa Barthelemy.

Heuerman is also the prime suspect in the death of Maureen Brainard-Barnes — with all four victims known collectively as the “Gilgo Four,” women who worked as escorts on Long Island.

The hulking architect was charged in part based on phone records, eye-witness accounts and a DNA match from a discarded pizza crust and napkin near his Midtown Manhattan office.

That sample, which was slightly degraded from being exposed to the elements, was a mitochondrial match to a hair found in burlap used to wrap Waterman’s body before it was dumped on Gilgo Beach.

State Supreme Court Justice Timothy Mazzei said he would give Heuermann’s lawyers until next week to file a response to the DA’s office request for a cheek swab.

Haddad acknowledged in court papers that the request could backfire.

“Should the defendant’s DNA from the [cheek swab] not match the DNA profile from the pizza crusts and napkin submitted for Rex Heuermann,” she wrote, “the defense would be presented with a potential trial defense.

“Thus, there is a clear indication that material and relevant evidence will be found and is crucial for trial.”