Jurors trying to decide the fate of a Manorville carpenter accused of killing two women more than 20 years ago told a judge Wednesday afternoon they could not reach a verdict.

But state Supreme Court Justice Richard Ambro told the jury — which has deliberated for 16 hours over three days — to keep deliberating in Riverhead.

“This was a long jury trial,” Ambro told jurors, noting that jury selection began April 17 and that there was almost eight weeks of testimony. “I’m going to direct that you continue deliberations.”

And so they did, and will continue Thursday.

The jury is weighing two counts of second-degree murder against John Bittrolff, 50. He is accused of strangling and bludgeoning Rita Tangredi, 31, of East Patchogue and Colleen McNamee, 20, of Holbrook. He was arrested in 2014 after DNA linked him to semen recovered from the bodies of both women, who worked as prostitutes.

Tangredi was killed Nov. 2, 1993, off a dirt road that is now Esplanade Drive in East Patchogue. McNamee was found south of the Long Island Expressway service road in Shirley, just east of the William Floyd Parkway, on Jan. 30, 1994.

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Earlier Wednesday, the jury asked Ambro for the definition of reasonable doubt, how to evaluate circumstantial evidence and the “process of listening to other jurors with an open mind.”

He obliged with those instructions.

The case against Bittrolff is entirely circumstantial. Other than his DNA, there was no evidence presented during the trial that linked Bittrolff directly to the killings. No witnesses saw him with the women or in the areas where they were killed. He insisted on his innocence from the moment he was told of the accusations.

Jurors have also viewed some of the evidence in the case, including video of detectives questioning Bittrolff after his arrest and crime scene photographs from the killings.

They also asked to listen to a readback of testimony about DNA from other men found in a semen stain on McNamee’s pants. Attorneys on both sides argued that the stain was helpful to them.