A former radio DJ accused of groping Taylor Swift before a concert testified Tuesday that he may have touched the pop superstar’s ribs with a closed hand as he tried to jump into a photo with her but insisted he did not touch her backside as she claims.

David Mueller told jurors at the civil trial on dueling lawsuits filed by Mueller and Swift that he and the singer were trying to reach around one another and “our hands touched and our arms touched” during a photo opportunity he estimated lasted no more than 40 seconds.

Under questioning by his attorney, Mueller said he may have touched Swift’s “rib cage, or rib, or ribs”.

The 2013 photograph of Swift, Mueller and Mueller’s girlfriend taken at the pre-concert event in Denver is a key piece of evidence in Mueller’s suit claiming he was fired after being falsely accused by Swift. He is seeking at least $3m.

The photo shows Mueller with his hand behind Swift, just below her waist. Both are smiling. Her lawyers have called the photo “damning” proof that Mueller groped her.

Mueller’s lawyer, Gabriel McFarland, showed jurors the photograph during his opening remarks and they looked at the image on their computer monitors while he spoke.

“If you look at that photograph, his hand is not underneath Miss Swift’s skirt, and her skirt is not rumpled in any fashion,” McFarland said, noting that no one on Swift’s concert team saw anything amiss.

Mueller also testified that one of his station bosses, Hershel Coomer, told him that he had met Swift earlier before the show and that “he told me that he had his hands on her butt”.

Mueller said: “I thought he was just telling me one of his stories.”

Coomer is expected to testify at the civil trial.

Swift has said she is positive it was Mueller who groped her.

Swift has counter-sued Mueller, claiming sexual assault. She is seeking a symbolic $1, saying she wants to serve as an example to other women who have been assaulted.

In his opening statement, Douglas Baldridge, an attorney for Swift, told jurors that his superstar client was “absolutely certain” she was sexually assaulted and will prove it in court.

Baldridge also asked what possible reason Swift would have to make up an allegation. “That’s the one and only story we have to tell you, that Mr Mueller grabbed her rear end,” he said.

Mueller’s attorney told jurors that inappropriate touching is wrong, but falsely accusing someone of the offense is equally unacceptable.

Baldridge disputed that description of the incident and instead called it an “assault”.

He also emphasized the age difference between Mueller, then 51, and Swift, then 23.

Swift is also expected to testify in the case, along with members of her entourage.

The case is being heard by a jury of six women and two men, most appearing to be over 30.

Mueller, wearing a smoke gray jacket and a white shirt, sat in court with his back to Swift and her mother, Andrea Swift.

Potential jurors were asked about everything from whether they or their relatives had ever been inappropriately touched or wrongfully accused of groping someone to whether, and to what degree, they were fans of Swift.

One man who was not selected told the US district judge William Martinez on Tuesday that he was not necessarily a fan, “but her music is catchy and it’s good vibes”. The judge laughed and said: “Very good.”

The case is being heard in federal court because Swift and Mueller live in different states – Swift in Nashville, Tennessee, Mueller in Colorado – and damages at stake exceed $75,000.

The trial is expected to last about two weeks.

About a dozen fans lined up outside the courthouse, including three high school students who showed up before dawn for a pass allowing them inside to watch the civil trial.

“I love how she’s suing him for $1 because she doesn’t need the money but she wants to make it a point that women don’t need to take this,” said Vega Zaringlee, 12.