SAN JOSE — One of the most confounding aspects of an alleged rape victim’s accusation against an on-duty San Jose police officer was her claim that he assaulted her while wearing a cumbersome bulletproof vest that many cops dislike even having to put on for work.

But on the first day of Officer Geoffrey Graves’ preliminary hearing Monday, his ex-girlfriend testified that he frequently wore the vest in bed with her while they played certain sex games.

“He kept his vest on a dozen times,” said the woman, whose identity was not released by the judge, lending more credence to the alleged rape victim’s account.

Graves, 39, is charged with one felony count of raping a woman he met on a disturbance call and two felony counts of roughing up his ex-girlfriend. He has pleaded not guilty and is free on $100,000 bail. He has been on paid administrative leave since his arrest last March.

Monday, Graves rejected an offer by the Santa Clara County District Attorney’s Office to plead guilty or no contest as charged, or face the possibility of even more serious allegations being added to the criminal complaint.

If Graves is convicted of the current charges, he would face up to 12 years in prison. But prosecutor Carlos Vega warned Graves that the consequences could be worse if Superior Court Judge JoAnne McCracken holds him over on the existing charges, as expected.

“There is no guarantee that the (charges) will be exactly the same,” Vega said in court. “The District Attorney’s Office is exploring some serious allegations.”

Vega declined to elaborate on the possible new charges. But experts say prosecutors could add a gun enhancement because Graves was armed with his department gun at the time of the alleged sexual assault, potentially extending his maximum sentence to life in prison.

The rape charge against the officer stems from a Sept. 22 family disturbance call. The woman, who is in the country illegally, did not report the incident until she was arrested three weeks later on suspicion of drunken driving.

Prosecutors have said they have DNA evidence bolstering the sexual assault charge and that the woman never requested nor was given leniency in exchange for reporting Graves. She pleaded no contest to the DUI charge and was sentenced to three years’ probation, nine days in county jail if she violates probation and eight days on the weekend work program, most likely cleaning up freeways. She also was ordered to pay fines and fees of about $1,900. She has no prior criminal record, according to court documents.

According to court documents, the sexual encounter between her and Graves came after police responded to a call about the argument she and her husband were having. No arrests were made during that call. She chose to stay at a nearby motel that night where she had worked as a maid and was escorted by two officers, including Graves.

Investigators have said the woman checked into a room, and eventually one of the officers left to answer another police call, but Graves stayed behind. After waiting a short time, police said, Graves returned to the woman’s room, overpowered her and “forcibly engaged in sexual intercourse with the victim before leaving the hotel approximately 10 minutes later,” according to court documents. He took off his shirt but wore his bulletproof vest, which investigators confiscated from his police locker.

In court Monday morning, Graves’ former girlfriend testified that when they first began dating in late 2009, they seemed to have a lot in common. She is a San Jose police radio dispatcher who was going through a divorce and he was also newly separated, she said.

But Graves started losing his temper at her frequently during their 3 1/2 year relationship, she said, estimating he cursed and “put his hands” on her about 12 times. She said the arguments often took place in a back room at his mother’s house in Gilroy, where he was staying, or in her Morgan Hill home.

Graves prevented her on more than one occasion from leaving a room by pushing her down on the bed or blocking the door with his body, she testified. Once when she was trying to drive away, he “ripped” the keys out of her hand, cutting her left index finger, she said. The woman who says he raped her also reported that he threw her down on the bed and prevented her from leaving the motel room.

The day the woman says she was raped, Graves came home from work hours late and abruptly began moving out, his ex-girlfriend said.

“He started crying,” the dispatcher said. “He seemed to be rambling. He said, ‘Things are not working out between us. It’s not you, it’s me.’ ”

Under cross-examination by Graves’ lawyer, Darlene Bagley Comstedt, the woman acknowledged that the officer had reason to be upset because the couple had discussed moving in together full time, but she didn’t want to.

“I was not confident,” she testified, “that him moving in was 100 percent a good idea. Because of his anger … I was not sure meshing our lives closer together was a good idea for our children.”

The alleged rape victim is scheduled to testify Tuesday.

Contact Tracey Kaplan at 408-278-3482 or follow her at Twitter.com/tkaplanreport

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