On its fifth day of deliberations, a Manhattan jury deadlocked on the question of whether drunken, now-ex-cop Michael Pena actually raped a terrified schoolteacher during a random gunpoint attack in Inwood last summer, leading the judge to end the trial.

Pena had already been convicted, yesterday, on the bulk of the charges against him, including the top charge of predatory sexual assault and of sexually violating the woman in ways other than rape.

But today, the victim broke into sobs as the jury forewoman repeatedly announced it had reached “no verdict” on four remaining rape-related charges in the hideous case.

Ultimately, their indecision on the rape charges may be moot to everyone but the still-shattered victim.

With yesterday’s partial verdict, Pena is already heading to prison for at least 10 years, the mandatory minimum time in a cage for predatory sexual assault, the indictment’s top charge; a parole board could then keep him in for as long as life.

The maximum sentence the judge can impose is 25 years to life, meaning it would be 25 years before Pena would even see a parole board.

Prosecutors have not signaled whether they will retry the rape charges. A May 7 sentencing date has been set on the convictions, and DA Cyrus Vance, Jr. said he will seek the maximum prison sentence for the disgraced 33rd Precinct officer.

““In this brutal attack against an innocent young woman, the defendant showed no mercy,” Vance said in a statement issued after the trial ended. “At sentencing, we will recommend that he receive none.”

Jurors had been battling with the rape charge since at least Monday, when they announced themselves at an “impasse” in a note sent out to the judge.

Then, in hush-hush discussions at the bench yesterday, one male juror could be overheard telling both sides and the judge that deliberations had turned contentious and personal, and that he was concerned that a juror named “Lloyd” had invoked the name of one-time DA political opponent Richard Aborn and seemed to be prejudiced against the DA’s office.

That juror — Lloyd Constantine, a former legal advisor to ex-Gov. Eliot Spitzer and a law partner of Aborn — was then grilled by the parties and the judge. Constantine conceded that he also had ties to Vance — having socialized with him on occasion. Records reveal that Constantine donated $5,000 to Vance’s campaign, and $5,000 to Aborn’s campaign, along with another $4,500 to Aborn from Constantine’s wife, Jan.

Constantine had revealed none of these ties to law enforcement during voir dire, explaining to the judge that he believed he was objective and didn’t want to be seen as dodging jury duty.

After the trial ended today, Constantine declined to say if he had caused a deadlock. But he said he was happy with how the deliberations went, noting, “I have not lost any sleep over this.”

Constantine also used the phrase “alleged crimes,” as in, “This was not fun. This was hard work. It was difficult, painful work. The nature of the alleged crimes were very painful to all of the participants and to the families and to the jurors.”

Finally, he said, “There’s no law that says a jury has to reach a verdict.”

What is clear is that arguments by defense lawyer Ephraim Savitt had cast doubt in the mind of at least one juror as to whether forcible intercourse was among Pena’s several heinous assaults upon the 25-year-old victim, a stranger to the drunken cop when he drew his service pistol and forced her into a backyard.

No forensics directly establish intercourse, the defense lawyer had noted. But lead prosecutor Evan Krutoy has countered that the circumstantial evidence is substantial against Pena, who was caught at the scene still zipping up his pants.

A passerby testified that, from 12 feet away, it appeared that Pena was having intercourse with the woman. Forensic investigators found the woman’s DNA on Pena’s genitals and Pena’s DNA on the woman’s underwear.

Then there was the compelling testimony by the victim herself. Two weeks ago the bespectacled, petite brunette took the witness stand to tearfully describe how Pena threatened to “shoot you in the f—ing face” if she called out or opened her eyes.

She was certain she’d been raped, she told jurors through her tears, because “It hurt.”