SANTA MONICA, CALIF. -- WARNING: This story contains graphic details

Sixteen-year-old Judy Huth was deeply distraught minutes after Bill Cosby is alleged to have sexually abused her on an afternoon in 1975 at the Playboy Mansion, her best friend at the time testified Wednesday.

“She said ‘I want to go, I wanna leave,’ she was crying," said Donna Samuelson, then 17 and now 64, the first witness in a Los Angeles County civil trial stemming from Huth's lawsuit against the 85-year-old comedian and actor.

Samuelson, who had been looking forward to spending the rest of the afternoon and evening at the mansion, was angry with her friend, until Huth explained herself.

“She said Bill Cosby had tried to have sex with her,†Samuelson said.

Huth told Samuelson that in a bedroom off a game room on the mansion grounds where the three had been hanging out and playing pool and arcade games, Cosby had tried to put his hand down her tight pants, then exposed himself, forcing Huth to touch him sexually, testified Samuelson, who had been distracted playing a game and was oblivious to what had happened.

Samuelson shot two photos of Cosby and Huth together that day that are central to the trial, and were shown constantly to the jury on day one. A clearly recognizable Cosby has a beard and red beanie.

A lawyer for Cosby called the sex abuse allegations “a complete and utter fabrication†and said the pictures are the only reason the case exists.

“This is about a plan hatched by Judy Huth and her estranged friend Donna Samuelson based on some photos,†lawyer Jennifer Bonjean said in her opening statement shortly before Samuelson took the stand. “You will learn Judy Huth has been trying to cash in on these photos for decades.â€

The trial represents one of the last remaining legal claims against Cosby after his Pennsylvania criminal conviction was thrown out by an appeals court last year, and his insurer settled many other lawsuits against his will. He is not attending the trial, and will not testify, but parts of a video deposition he gave shortly after the 2014 lawsuit was filed will be played.

Samuelson testified that Cosby had met the two girls on a film set at a Los Angeles area park a few days earlier, and invited them to come to a club where he would be playing tennis, then took them as a surprise to the mansion, telling them if anyone asked their ages to say they were 18, but no one did.

By the time Huth told her story to Samuelson, Cosby had left to attend an event with plans to return hours later, leaving the girls behind.

Samuelson said she asked her distraught friend if she wanted to go to the police or tell anyone else, Huth emphatically answered no. She convinced Huth to stay at the mansion.

“I thought it would calm her down to go swimming and stuff,†Samuelson testified. “I said, ‘We’ll leave as soon as he gets back.'â€

She said the mansion's butler brought the girls swimsuits in whatever style, size and colour they asked for, and they hung out in the mansion's famous grotto pool and ordered tequila sunrises. Then they had dinner in the mansion, sitting across from actor Peter Lawford.

They were tinkering on a grand piano when Cosby returned and put his arm around a horrified Huth. The girls promptly got up to leave, Samuelson said, but just then Playboy head Hugh Hefner and his magazine model girlfriend Barbi Benton walked in, and Cosby introduced them before they left.

Bonjean seized on the girls' staying at the mansion during her opening.

“Boy did Judy and Donna enjoy themselves. They stayed for 12 hours," Bonjean said. “There's no typical response to a traumatic event but partying at the Playboy Mansion does not seem consistent.â€

But in his opening statement, Huth's attorney Nathan Goldberg said in the months that followed, she was very much emotionally affected by the trauma, smoking pot in great amounts, getting into troubled relationships and suffering from anxiety.

“She was no longer the happy-go-lucky girl she had been,†Goldberg said.

The Associated Press does not normally name people who say they have been sexually abused, unless they come forward publicly, as Huth has.