Heidi Thomas was an aspiring actress in 1984, she said, when Bill Cosby offered her a drink during an acting lesson.

She drank it, passed out, and, she said, awoke to a naked Cosby forcing himself on her.

For decades Thomas stayed largely silent. But when Cosby was arrested a year ago for allegedly drugging and molesting Andrea Constand, Thomas reached out on Facebook.

"Girl, we've got your back," she said she wrote in a message to Constand.

Thomas is one of 13 women - among dozens nationwide to publicly accuse Cosby of sexual misconduct - who prosecutors want to call as witnesses at the entertainer's sex-assault trial next spring.

A few, like her, were young actresses seeking career guidance. Others met him during his travels as an entertainer. Some had agreed a decade ago to testify against him - in the civil case brought by Constand that ended in a settlement before trial.

But together, the Montgomery County District Attorney's Office contends, their testimony demonstrates Cosby's alleged attack on Constand followed a long-established pattern.

That's the argument prosecutors are expected to present during two days of hearings that start Tuesday in Norristown.

Cosby's lawyers have countered it would be unfair to introduce as evidence decades-old allegations that aren't just unproven but are so outdated they would be hard to disprove.

The argument awaiting Montgomery County Judge Steven T. O'Neill represents one of the central battles of the case, one that could transform Cosby's trial from a more traditional he-said-she-said sex-assault case to one that forever recasts an international celebrity once known as "America's Dad" as a serial sex predator.

In allegations spanning from 1964 to the 1990s, the 13 women allege that Cosby drugged and sexually assaulted them - in many cases after cultivating a relationship as a mentor or offering tickets to a show.

Wine and a pill

Among them is Therese Serignese, 59, of Florida, who says Cosby drugged and attacked her in a bathroom at the Las Vegas Hilton in 1976 after she met him in the gift shop. Another, Donna Motsinger, was a waitress at a Sausalito, Calif., restaurant in 1972 when she claims Cosby invited her to a show and gave her wine and a pill on the way there. She said he fondled her and she woke up at home the next day, nearly naked.

(The Inquirer typically does not identify sex-crime victims without their consent. But of the 13 women, 11 have publicly identified themselves as victims in lawsuits, news conferences, or media interviews, as has Constand.)

O'Neill will not hear testimony from the women themselves this week; the hearings will be limited to arguments from lawyers.

But how the prospective witnesses were chosen is likely to become a key part of the debate.

A certain type of witness

In a hearing last month, District Attorney Kevin R. Steele offered some insight into the process, asking the judge to take "a practical look" at how the women were drugged in a setting where Cosby "controls the environment" and had established relationships with them.

Constand, now 43, got to know Cosby when she worked as operations director for the women's basketball team at Temple University, where Cosby was a member of the board of trustees. The two became friends over time, and she later told police that she saw him as a father figure. Cosby says their 2004 sexual interaction at his Cheltenham mansion was consensual.

Patricia Steuer, a Cosby accuser from California, was interviewed by Montgomery County detectives but not asked to testify. She said it was clear they were searching for a certain kind of witness.

"They did say that the Prosecutor's Office had to decide which of the potential witnesses had stories that were closest to the story of Andrea Constand," said Steuer, who said she talked with detectives at her home for three hours, in an interview.

Pennsylvania law allows testimony about so-called prior bad acts if it establishes a common scheme or pattern of behavior by a defendant.

It can also be used to show "absence of mistake" in committing a crime. Despite Cosby's claim that his sexual contact with Constand was consensual, prosecutors could use other women's accusations to argue the pattern of behavior proves his intentions.

Defense lawyers have argued that Cosby, now 79, blind, and frail, is at a disadvantage to recall details and allegations stemming back decades, especially ones that were not reported to law enforcement at the time.

"We are left with reports that were prepared by their detectives just recently," Cosby's lawyer Brian McMonagle said at a hearing last month. He said some statements lack detail, suggesting only "sometime, somewhere, someplace Bill Cosby did something to me."

At least half of the 13 accusers have been represented by lawyer Gloria Allred, a fact Cosby's attorneys have also used to argue the women are seeking the limelight or payouts.

Allred has declined to comment on her contact with prosecutors or which of her clients might testify, except to say: "I am honored to represent potential witnesses and neither my clients nor I will be deterred by unwarranted personal attacks by Mr. Cosby's attorneys upon us."

One of her former clients, Beth Ferrier, said she did talk to detectives but was not asked to be a trial witness.

"I'm really glad that I'm not selected," said Ferrier, 57, of Colorado, in an interview last month. "I feel really terrible for any of the girls who are selected because I feel like, knowing Cosby, he is going to annihilate them. I know him, intimately and personally. He will do nothing more than try to destroy all of these girls."

In court filings, Cosby's lawyers have already revealed some of their research into the women's backgrounds in an attempt to undermine their credibility.

Of one accuser who has not come forward publicly, defense lawyers wrote in court filings that "she kept the sweatshirt he allegedly made her wear during the 'rape' like a treasured souvenir and, years later, even photographed herself wearing it when she was nine months pregnant with her child."

They say another accuser, Motsinger, dated a founder of the "Brotherhood of Eternal Love - aka the 'Hippie Mafia,' " a group that made LSD and smuggled drugs.

Support network

At the same time, some of the accusers have created their own support network. Some have become friends. More than one said they had also been in touch with Constand, who does not discuss Cosby with them.

Thomas, a 57-year-old music teacher and mother of three, lives in Colorado, half a continent away from Constand, who lives in Canada. She said that when she wrote Constand a supportive message on Facebook, Constand responded by congratulating her on her daughter's wedding.

Thomas said she spent hours with Montgomery County detectives last summer at her Colorado home. She sensed it was a vetting process, that they were looking for accusers who would be articulate on the witness stand.

She feels prepared to testify if the judge allows.

"There are so many of us who have gone on and found our voice as a result of saying, 'To heck with it all,' " Thomas told The Inquirer last month. "[The defense] can throw their slings and arrows at us. We've already been through all that. He can't hurt us anymore."

610-313-8116@Lmccrystal