In a victory for Bill Cosby, a Montgomery County judge ruled Friday that he would allow only one additional accuser to testify at the 79-year-old entertainer's sexual assault trial.

Judge Steven T. O'Neill offered little explanation for his decision to bar prosecutors from calling 12 other women whose testimony they hoped could establish a decades-long pattern of sexual misconduct by Cosby. In his one-page order, the judge said he had carefully weighed their potential value as witnesses against the threat that their unproven allegations might prejudice a jury.

The ruling effectively narrows the scope of the trial and settles  at least for the moment what had emerged as the central legal battle in Cosby's case.

Montgomery County District Attorney Kevin R. Steele had proposed a public airing of multiple instances — all too old to prosecute — in which Cosby allegedly drugged and sexually assaulted women.

Instead, the proceedings are now likely to play out largely as a he-said, she-said contest pitting Cosby's credibility against that of the case's central accuser, Andrea Constand, and a woman who says she was assaulted in a similar way by the entertainer in 1996 at a Los Angeles hotel.

Her account is the most recent of those put forth by the prosecutors' other witnesses. It also tracks most closely with the allegations Constand first reported in 2005, a year after she says Cosby drugged and attacked her at his Cheltenham residence.

The District Attorney's Office did not immediately say Friday if it would seek to appeal the ruling before trial, which O'Neill has said he plans to begin by June.

Steele, in a one-paragraph statement, called the decision "important, as the jury will now be allowed to assess evidence that is relevant to establishing a common plan, scheme and design of sexual abuse and an absence of mistake by the defendant."

Cosby's lawyers declined to comment Friday, but their client retweeted several news articles on the ruling, adding the hashtags "#PayAttention" and "#Keep Watching."

Many of the 13 women whom prosecutors had lined up to testify — culled from the more than 50 who in recent years have publicly accused Cosby of past sexual abuse — viewed their shot on the witness stand as a last chance to find justice for their decades-old allegations.

Steele had argued that their testimony was crucial to proving the celebrity once known as "America's Dad" was a serial sexual predator.

Cosby strenuously fought to block them from the courtroom, arguing that the allegations, some of which dated to 1964, were not only unproven but were too old and too vague to disprove.

Some of the women could not specifically recall being assaulted, but said they remembered waking up disoriented and feeling as if something had happened to them, Cosby lawyers Brian McMonagle and Angela Agrusa argued at a hearing last year. Others could not remember in what year their alleged attacks occurred.

The defense lawyers also questioned links that more than half of the accusers had to celebrity lawyer Gloria Allred. They claimed she shaped their testimony to bolster prosecutors' case and set her clients — and herself — up for large payouts in civil lawsuits to come.

Allred, who also represents the lone accuser whose testimony O'Neill cleared for trial, said in a statement Friday that "even though [the others] will not be able to testify in this case, they have been very important in the effort to seek justice."

Like many of the other 12 witnesses prosecutors lined up, the woman slated to testify has previously shared her story publicly. Unlike the others, she did so under a pseudonym — "Kacey" — and has not made any public appearances.

Now 55, she claims she first met the TV star in the '90s while working as an assistant for the William Morris Agency, which counted Cosby as a top client. Like Constand, the woman alleges she had no desire to be an actress but viewed Cosby as a father figure who relished in dispensing career advice.

According to court filings, they quickly formed a friendship, with Cosby welcoming visits from her, her children, and other family members. At times, the woman would later tell investigators, she felt uncomfortable in his presence.

He once invited her to his home to audition for a role on The Cosby Show, and urged her to practice a scene with him that ended with a passionate kiss, according to court filings. She refused.

Prosecutors say "Kacey's" alleged assault occurred when she arrived for a lunch date in 1996 at Cosby's bungalow at the Hotel Bel-Air in Los Angeles to find him dressed only in a robe and slippers. He allegedly plied her with red wine and offered her a pill to relax, purportedly saying, "Would I give you anything to hurt you?"

The woman says that she accepted the pill after refusing several times, and that Cosby demanded she open her mouth and lift her tongue to prove she had swallowed it. Soon after, she alleges, she began to fade in and out of consciousness, and later woke up face down in Cosby's bed with him naked and on top of her.

"For those who will choose not to believe that I am speaking the truth of what happened to me, please know that I wish it were not true," she said in a January 2015 statement. "But I lived it and know that it is true. I no longer have to feel alone with this secret."

Constand, too, alleges that her assault came after Cosby offered her pills. She told police he gave her the unmarked medication when she complained of a headache and then molested her as she began to pass out.

Cosby has maintained his encounter with Constand was consensual and denied ever sexually assaulting anyone.

In court filings, his lawyers have pinpointed key differences between Constand and "Kacey," offering a glimpse of how they might attack her testimony in cross-examination.

Chiefly, they say, "Kacey" is the lone African American among the 13 accusers prosecutors had put forth. She is also the only accuser who was older than Constand at the time of her alleged attack.

"She remembers some lotion and touching," they wrote in a motion last year, "but has no memory of having sexual intercourse with Mr. Cosby."

Though O'Neill's ruling Friday was largely a win for Cosby, some legal experts viewed the judge's decision as a conservative move, meant to protect a potential conviction on appeal.

Pennsylvania law allows testimony about "prior bad acts" only if it establishes a common scheme or pattern of behavior by a defendant and does not unfairly prejudice a jury against the accused.

A miscalculation on that front could unravel the case at the appellate level, as it did in perhaps the best-known recent case in which evidence of past uncharged crimes played a central role – the child endangerment trial of the Philadelphia Roman Catholic Archdiocese's former secretary of the clergy, Msgr. William J. Lynn.

Two state appellate courts have found that the Philadelphia judge in that trial overstepped by allowing jurors to hear evidence of 21 other purported, decades-old incidents of sex abuse by priests that were allegedly covered up by the archdiocese.

O'Neill "was obviously conscious of what the Superior Court said" in the Lynn case, said Jeff Lindy, one of the monsignor's lawyers at trial. "He's got to be thinking that with all the attention on this case, the last thing he wants is to have the case come back to him because he let some of these witnesses in."

Clues to the judge's next big decision in the case could come as soon as Monday.

That's when Cosby is due to return to O'Neill's courtroom for arguments on his request to change the location of his trial or bring in jurors from another county because of what he has described as overwhelming negative publicity in Montgomery County.