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(CNN)- A former prosecutor who declined to bring charges against Bill Cosby a decade ago said Wednesday that he wishes he could’ve nailed the comedian on an allegation that he drugged and molested a woman at his Pennsylvania home.

Bruce Castor also told CNN that he believed Cosby — a beloved figure who, with his wit and boyish smile, has charmed audiences as a family-friendly stand-up comic, the voice of Fat Albert, the host of “Picture Pages” and the star of a wildly popular eponymous sitcom — lied to authorities.

In January 2004, Andrea Constand, then a 31-year-old staffer for the women’s basketball team at Temple University, Cosby’s alma mater, was at the comedian’s Cheltenham, Pennsylvania, home when Cosby provided her medication that made her dizzy, she alleged the following year.

She later woke up to find her bra undone and her clothes in disarray, she further alleged to police in her home province of Ontario in January 2005.

Cosby’s attorney in the case, Walter M. Phillips Jr., called the allegations “utterly preposterous” and “plainly bizarre” at the time, yet in a civil filing, Constand’s lawyers said they had found 13 “Jane Does” with similar stories. Cosby settled the civil suit in 2006.

The terms of the settlement were not disclosed, but when journalist and publicist Joan Tarshis came forward with another similar story this weekend, Cosby attorney John Schmitt denied her claim and others’, labeling them “decade-old, discredited allegations.” Schmitt later amended that statement to say he wasn’t referring to Constand, who resolved her differences “to the mutual satisfaction of Mr. Cosby and Ms. Constand years ago.”

‘I couldn’t check her blood’

Castor, who was the district attorney for Montgomery County, Pennsylvania, when Constand came forward in 2005, now tells CNN he thought Constand was credible, and he thought Cosby was evasive in his interview with prosecutors. Castor, whose assistants interviewed Cosby, said he felt the comedian was setting up a defense that Constand was at his house on her own volition and that anything occurring between them was consensual.

“Back then, the desire on our part to move forward was pretty strong,” he said. “The problem with the case was she waited a year until she told police about it.”

This left Castor no way to corroborate Constand’s allegations, he said. He couldn’t check her blood, urine, hair or fingernails for traces of drugs, he couldn’t obtain hair or fiber for analysis, and he couldn’t obtain a warrant to search Cosby’s home for evidence.

“I had a theory that Cosby had drugged the woman using something to make her sleepy and to make her defenseless or unable to recall what happened, but because of the delay, I couldn’t check her blood,” he said.

Of Cosby’s interview with prosecutors, Castor said, “I thought he was lying. I thought he was evasive, and I thought that those things would be of value if I had another piece (of evidence) to go forward with.”

The case would have come down to she said, he said, and while Castor felt strongly that Constand was telling the truth, her statements alone were not going to be enough to convict Cosby, the ex-prosecutor said.

“Did I think he probably did something inappropriate? Yes. Did I think that I could prove it beyond a reasonable doubt based on available, credible and admissible evidence? No, I didn’t,” he said.

Castor released a statement on his office’s website in 2005, saying that he found that “insufficient credible and admissible evidence exists upon which any charge against Mr. Cosby could be sustained beyond a reasonable doubt.” Constand’s attorney filed the civil suit two weeks later.

Latest in line of accusations

Castor’s account comes a day after former supermodel Janice Dickinson became the latest of a handful of women to accuse the 77-year-old comic of sexual assault publicly. She told “Entertainment Tonight” that Cosby raped her in 1982 after giving her a pill and a glass of red wine during a dinner in Lake Tahoe.

“The last thing I remember was Bill Cosby in a patchwork robe, dropping his robe and getting on top of me. And I remember a lot of pain,” she said.

Dickinson did not return a telephone call from CNN seeking comment, but Cosby has repeatedly said previous allegations are untrue. He has never been prosecuted.

His attorney, Martin Singer, addressed Dickinson’s allegations specifically in a statement, calling them a “fabricated lie” and saying they contradicted what she wrote in her autobiography and what she said during a 2002 New York Observer interview.

Since 2005, several women have come forward with remarkably similar stories about being drugged and sexually assaulted by the comedian. This year, the accusations resurfaced, and earlier this month, a seemingly harmless post on Cosby’s Twitter account turned them into a social media storm.

After the accusations gained steam again, one of his accusers, Barbara Bowman, turned to the public once more with an article in The Washington Post and interviews with CNN. Bowman alleged she was drugged, then raped, though she said she never saw drugs.

“I woke up out of a very confused state not in my clothes,” she said.

On Saturday, NPR broadcast an awkward interview with Cosby in which he didn’t utter a word when repeatedly asked about the accusations.

NPR host Scott Simon filled the airtime by saying Cosby was just “shaking his head no.”