A jury found a city cop guilty of sexual assault Tuesday but deadlocked on whether he raped a Bronx schoolteacher after the trial was thrown into chaos by revelations that one juror was a tennis buddy of the Manhattan DA.



That juror was Lloyd Constantine, a prominent lawyer and player in city legal circles who had once been an adviser to disgraced former Gov. Eliot Spitzer.



Constantine never mentioned he and Cy Vance Jr. were pals — or that he gave the district attorney a $5,000 campaign contribution in 2008 — during jury selection.



When asked why, Constantine brazenly told the judge he felt he wouldn't be biased either way and that he'd passed his "own subjective test."



The discovery of Constantine's connections came just before the jury handed down a partial verdict against the officer, finding him guilty of predatory sexual assault.



Pena was fired by the NYPD and will lose his pension after his felony conviction.



He sat silently as the eight men and four women on the jury announced their verdict. But his 25-year-old victim burst into tears when the jury declared it still hadn't reached a verdict on the four rape counts.



The fact that Pena was convicted of forcing her to submit to oral and anal sex — six charges that could send him to prison for life — appeared to be little comfort to her.



Constantine's presence on the panel was all the more surprising because the DA himself watched the closing arguments in the trial and his buddy sat in the front row of the jury box.



Vance's spokeswoman said the DA didn't spot Constantine in the courtroom.



She said they began looking into him after another juror complained he was trashing the prosecution's case and mentioned that he worked with Richard Aborn, who ran against Vance for DA in 2009.



When they realized Constantine's link to Vance, they immediately reported the potential conflict of interest to Manhattan Supreme Court Justice Richard Carruthers.



Pena's lawyer said he too doubts Vance would have been able to see Constantine.



"Vance is going to start eyeballing the jury?" Ephraim Savitt said. "He was all the way back there in the back of the courtroom and the place was packed."



Constantine's chutzpah came as no surprise to Darren Dopp, a former Spitzer spokesman. He said Constantine was one of Spitzer's advisers.



"He is not a team player and he was a very arrogant individual," said Dopp. "Lloyd would shrug at being called arrogant. He would say I have a right to be."



Dopp said most Spitzer hands have shunned Constantine since he published a memoir blaming the governor's downfall on the fact they stopped playing squash together.



"When Lloyd joined that team he became a very disruptive force," said Dopp, who is also on the outs with Spitzer.



Constantine and the rest of the bitterly divided jury will resume deliberating after Carruthers told them he was not ready to settle for a partial verdict.



"Please be respectful to one another," he said.



But Carruthers allowed the alternates to go home — and they wasted no time escaping the courthouse.



"It was a difficult process, it was trying," said Pat Lee as she rushed out.



Pena, 27, was charged with 10 counts total. He has admitted assaulting the woman and threatening to shoot her in the face but denies raping her.



Savitt said they have not decided yet whether they will appeal the convictions, but might ask for a mistrial if the jury doesn't reach a final verdict.



"There is a lot of bickering going on," Savitt added. "It seems to be a remaking of '12 Angry Men.'"



With Kerry Burke, Glenn Blain and Rich Schapiro



mgrace@nydailynews.com