Bill Cosby
© Michael Bryant โ€” Pool/Getty ImagesBill Cosby, center, being led to court by an aide in Norristown, Pa.
Some knew him for only a day. Others built friendships over months, even years, and introduced him to their mothers, an aunt, even a 9-year-old son, they say.

But all 13 women say the same thing: Bill Cosby finally gave them a pill, or some other intoxicant, sometimes hidden at the bottom of a fizzing glass of champagne or a glass of wine or soda, and they awoke hours later having been sexually abused.

Prosecutors in Montgomery County, Pa., announced this month that 13 women, selected from a larger pool of nearly 50 who say Mr. Cosby assaulted them, have now agreed to come forward and testify at a long-anticipated criminal trial next June.

The prosecution has asked the court to allow the women to testify, and the judge's ruling, expected in coming months, will be critical to Mr. Cosby's fate.

If the testimony is allowed, the prosecution's case would be bolstered by its ability to bring forth accuser after accuser with accounts similar to that of Andrea Constand, the former Temple University basketball staff member whose accusations are at the center of the June trial. Prosecutors have charged Mr. Cosby with drugging and sexually assaulting Ms. Constand at his home near Philadelphia in 2004.

"It could be the most important ruling in the case," said Benjamin Brafman, a defense lawyer in New York who is not involved in the Cosby case. "It is no longer just one person making the allegations."

For the women, their testimony could represent a final legal opportunity to address what they contend was Mr. Cosby's criminal behavior. Most never came forward decades ago, when they say the episodes occurred. Even civil cases against him have largely been prevented by statutes of limitation.

But this sort of evidence is not often admitted in criminal cases. Ordinarily, prosecutors in Pennsylvania and most other states cannot introduce evidence or accusations of prior bad behavior. It is viewed as too prejudicial for a jury as it sifts through the facts of the case that is actually before it. Mr. Cosby's legal team said it would fight to block the women from testifying.

There are circumstances, though, in Pennsylvania and other states where such evidence is permitted โ€” for instance, when it shows conduct so similar it can be argued that it demonstrates a common scheme or plan, a kind of unique fingerprint of criminal behavior.

In the Cosby case, prosecutors say in court papers that the women's accounts form such a pattern โ€” that he befriended each of them, mentoring some, drugging and assaulting them all, just as, they say, he did Ms. Constand.

Twelve of the 13 women say Mr. Cosby offered them alcohol or pills or both. One woman said she drank a glass of soda, which she says she believes was laced with a drug.

Ms. Constand says Mr. Cosby had evolved into her mentor, invited her to his home, gave her pills and wine, then molested her while she was incapacitated. Mr. Cosby has denied all of the women's charges.

Prosecutors did not name the women in their court papers. But 11 of them โ€” Janice Baker Kinney, Therese Serignese, Linda Kirkpatrick, Heidi Thomas, Margie Shapiro, Lise-Lotte Lublin, Donna Motsinger, Rebecca Lynn Neal, Linda Brown, Cindra Ladd and a woman who identified herself only as Kacey โ€” have previously come forward to publicly detail their allegations, and their identities are clear from the information made public in the court filing.

One woman, Ms. Serignese, says Mr. Cosby assaulted her in 1975 or 1976 when she was 18 or 19 after they met in a hotel gift shop and he invited her to a show and gave her pills.

Another, Ms. Motsinger, has accused Mr. Cosby of assaulting her in 1972, a time when she was working at a restaurant in Sausalito, Calif. He took her to one of his shows but then assaulted her after giving her wine and a pill, she said.

Ms. Motsinger, now 75, said she could not discuss why she agreed to testify but said of the trial, "It's one step closer to justice."

While most of the women who have agreed to testify had once been public with their identities and accusations, even going so far as to participate in news conferences, they did not want to comment further at this point.

Patricia Leary Steuer, 60, who has accused Mr. Cosby of drugging and assaulting her but is not among the 13 women, said, "None of us want to jeopardize the outcome of the trial by speaking in a way that would make the prosecutor's job more difficult."

She added, "We're all voluntarily being very quiet."

Two of the 13 women, a former flight attendant and a woman identified in court papers as having worked at the Playboy Club in New York, do not appear to have ever come forward publicly.

The decision on whether to admit the testimony of the women will be made by Judge Steven T. O'Neill, who, legal experts said, may choose to include the testimony of all 13, or fewer, or reject altogether any of their accounts as evidence. The judge may wait until Ms. Constand gives her own testimony at trial: If her own evidence is strong enough, he may decide that there is no need to include the other women's accounts, the experts said.

Efforts by prosecutors to introduce "prior bad acts" evidence are limited, said Lynne M. Abraham, a former Philadelphia district attorney and judge, because they can backfire. Even in cases in which defendants are convicted, there is the chance the decision will be overturned on appeal when a higher court rules that including other, prior evidence was, in fact, prejudicial.

That happened in a recent case involving a senior official in the Roman Catholic Church in Philadelphia who was convicted on charges related to failing to stop child sexual abuse by some priests. Prosecutors introduced historical evidence, but appellate courts later decided that the evidence had impaired the jury's ability to deliver a fair verdict.

"It is sometimes successful, and sometimes it falls flat on its face," Ms. Abraham said.

Mr. Cosby's lawyers say they will show that the women's testimonies fail to meet the criteria for inclusion, because, they say, for example, the accusations are decades old or uncorroborated.

Isabelle A. Kirshner, a criminal defense lawyer in New York, said a judge would also have to take into account the time and resources involved in cross-examining so many accusers. "He will ask, 'Do we really want to have in effect 13 separate trials?'" she said.

Detectives who reopened the investigation into Ms. Constand's allegations last year interviewed nearly 50 women who brought accusations against Mr. Cosby, according to court documents. Kevin R. Steele, the Montgomery County district attorney, chose to offer the testimony of just 13 in the interests of "judicial economy," the documents say.

One of the 13 is a former masseuse; another was a cocktail waitress. Some were models and aspiring actresses. According to prosecutors, the women often met Mr. Cosby through their work, and he would win their trust with career advice, or invitations to dinner โ€” as, they say, happened in Ms. Constand's case.

At least nine of the 13 women are white, and Mr. Cosby's legal team has complained that the prosecution is tainted by racial bias. A statement from his team this month took particular issue with Gloria Allred, a feminist lawyer with a knack for drawing media attention, who presided at news conferences in which many women aired their accusations against Mr. Cosby. Ms. Allred had at one time represented at least seven of the 13 women planning to testify.

"She calls herself a civil rights attorney, but her campaign against Mr. Cosby builds on racial bias and prejudice," the statement said.

Ms. Allred responded with her own statement: "This is not an issue of racial bias. Instead, it is an issue of whether or not Mr. Cosby has committed acts of gender sexual violence."

Joseph Cammarata, a lawyer for Ms. Serignese, said any effort to undermine the prosecution's case by focusing on race or attacking the characters of the women would be quickly overshadowed by the facts.

"There is a certain pattern here: It is very compelling and powerful," he said. "At the end of the day, did it happen, or did this not happen?"