A Suffolk County judge sided with prosecutors and ruled Gilgo Beach murders suspect Rex Heuermann must provide a DNA sample, according to a court ruling filed Wednesday.

"The Court finds that contrary to the defendant's contentions, there is probable cause to believe that the defendant committed the crimes charged and, therefore, a basis to compel the buccal swab," Judge Timothy Mazzei wrote.

He further wrote that "the Court finds that a comparison of the defendant's sample with the evidence obtained," including a hair found on a victim he is accused of killing and "the DNA found on the pizza crust and napkin, will yield probative material evidence, whether it is inculpatory or not."

The ruling comes after prosecutors submitted a request to the court to obtain a buccal swab -- otherwise known as a cheek swab -- of DNA, according to the Suffolk County District Attorney's office.

The order grants the prosecution's motion to obtain the oral swab sample in the presence of his attorney. Notably, the judge's order states that buccal swabs were previously obtained from Heuermann's wife and two children "upon consent for further DNA analysis."

Heuermann is charged with three counts of first-degree murder in the killings of Melissa Barthelemy in 2009 and Megan Waterman and Amber Costello in 2010, according to Suffolk prosecutors.

He is also the prime suspect in the 2007 disappearance and death of a fourth woman, Maureen Brainard-Barnes, according to a court document from prosecutors. Heuermann has not been charged in connection with that fourth homicide, but the investigation "is expected to be resolved soon," the document says.

Through his attorney, he has refuted the charges against him.

On Tuesday, Suffolk County Sheriff Errol Toulon told CNN's Erin Burnett that obtaining DNA is "extremely important to this case," adding he has "no doubt" Heuermann killed the three women he is accused of murdering.

A key break in the case came in January, when investigators recovered Heuermann's DNA from pizza crust that was thrown away in a Manhattan trash can. That DNA matched DNA from a male hair from the bottom of a burlap sack that the killer used to wrap one of the victim's bodies, according to prosecutors.

Authorities already have DNA samples from the suspect's wife, Asa Ellerup. Those samples were collected from bottles inside a trash can outside the couple's shared home and were linked through mitochondrial DNA testing to hairs found on or near three of the slain victims.