A sexual assault trial began Monday against an RCMP constable accused of sexually assaulting a young woman while she was in custody at the Red Deer detachment.

Jason Andrew Tress, 32, pleaded not guilty to sexual assault and breach of trust.

Crown prosecutor Photini Papadatou alleges that on July 1, 2016, Tress coerced the woman, forcing her to show him her breasts while she was his prisoner under his custody at the RCMP detachment.

"At the end of the day you're going to have to decide if you believe this young lady," Papadatou told Court of Queen's Bench Justice Grant Dunlop.

The only witness who testified Monday was the complainant, Melissa Heinrichs. The 22-year-old did not request a publication ban on her identity.

"This case is all about the credibility of that witness," defence lawyer Robb Beeman said. "Const. Tress says this did not happen."

According to an agreed statement of facts, Heinrichs and her boyfriend at the time, Keifer Collins, were living at the Travelodge in Red Deer. A hotel staff member spotted firearms in their room and called RCMP.

Tress and two other RCMP members were sent to the hotel to investigate.

When officers discovered weapons hidden under a stairwell, they took Collins and Heinrichs into custody.

Heinrichs testified she was very upset when Tress handcuffed her and put her in the back of the police vehicle.

Melissa Heinrichs, 22, walks towards the Red Deer courthouse to testify at a sexual assault trial. (Janice Johnston/CBC )

"I was pretty hysterical. Emotional," Heinrichs said.

She said while the two of them were alone in the vehicle, Tress made some comments she described as vulgar, referring to some of her body parts and his state of sexual arousal.

"He was saying that an old man could dream of being with a young 19-year-old girl like me."

Heinrichs said once she got to the detachment, she was searched by a female officer. Then Tress removed her from a cell and took her to the fingerprint room.

According to the agreed statement of facts, they were in the room for 22 minutes. The door was closed and one officer who tried to open the door was unable to gain entry.

There were no cameras in the fingerprint room.

Heinrichs was not fingerprinted.

'He was just being creepy'

She said Tress asked her to stand with her back against the wall, then asked her to show him her breasts, "to humour an old man."

Melissa Heinrichs was allegedly sexually assaulted on July 1, 2016 while being detained at the RCMP detachment in Red Deer. (Janice Johnston/CBC )

Heinrichs said she was uncomfortable with the request, but felt like she was in a vulnerable position since she was under arrest and unable to leave.

"It was kind of an awkward conversation. I wasn't sure how to say no," Heinrichs testified. "So I asked, 'Aren't there cameras in this room?' He said, 'No.' That no one was going to see."

She alleges Tress repeated his request many times over the 22 minutes until finally, she relented.

"When I did do it eventually, it was a quick thing to appease him," Heinrichs said. "Then I asked if I could go back to my cell."

The prosecutor asked her to describe the constable's behaviour during their encounter in the fingerprint room.

"He was just being creepy, for lack of a better word," Heinrichs said. "Unprofessional."

She admitted that at the time of the encounter, she was suffering from severe drug withdrawal symptoms. Heinrichs told the court that in July 2016 she had been addicted to fentanyl and crystal meth for three years.

"I hadn't used since I had woken up," she testified. "I was shaking violently, sweating, cold chills. I just wasn't my best."

Heinrichs was released without being charged. Under cross-examination, she admitted that once she was let go later that day, she went back to using drugs.

Her boyfriend was charged and kept in custody. Heinrichs said a few days later, she told him what the officer had asked her to do while she was at the RCMP detachment. Collins is expected to testify Tuesday.

She had no plans to tell anyone in authority, but on July 12 a pair of RCMP officers in a section working with people who live high-risk lifestyles paid her a visit.

"They had been pretty friendly to me and helpful," Heinrichs said. "When they were leaving, I blurted out, hypothetically, if someone had been detained and had been coerced to expose themselves — what would you suggest they do?"

Her allegation quickly became the focus of an investigation launched by the Alberta Serious Incident Response Team. ASIRT investigators questioned her on July 25, 2016.

Under cross-examination, Heinrichs admitted she was under the influence of fentanyl and crystal meth both times she was questioned by police about the alleged incident.

She insisted the drugs did not make her paranoid or delusional.

'I don't know what you want from me'

When Heinrichs gave evidence at a preliminary hearing last October, she said she was early into her recovery and living drug-free. But now she admits she lied at the earlier hearing.

Last fall, Heinrichs testified that Tress tried to grab her buttocks and was breathing down her neck as he took her fingerprints.

On Monday she told the court, "I really don't know why I said that. I'm not trying to make false allegations. It wasn't true."

Heinrichs fought back tears on the witness stand.

"I don't know what you want from me," she told the defence lawyer.

"This suggestion Mr. Tress asked you to show him your breasts never happened," Beeman said.

Jason Tress enters the Red Deer courthouse for his sexual assault and breach of trust trial. (Janice Johnston/CBC)

"Whatever the f--k you want to believe," Heinrichs replied angrily.

She looked at the accused and pointed toward him.

"You know what happened," she said.

The trial is scheduled to last five days. Tress faces another breach of trust charge, also dating back to 2016, involving another woman. In addition, he faces one count of sexual assault involving a third woman, stemming from an unrelated incident in 2012.

Tress will be tried separately on those charges, following an application by his lawyer.

