In response to Swift's lawsuit, which claims sexual assault, the former radio DJ host is accusing the 27-year-old singer of causing him to lose his dream job at 98.5 KYGO and ruining his reputation.
Swift sued Mueller, accusing him of inappropriately touching her during the meet-and-greet.
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".
Mr Baldridge did get Mueller to concede that various supervisors with KYGO and its parent firm had discussed the possibility of letting him go even before the encounter with Swift.
Douglas Baldridge, the attorney for the Swifts, showed the jury photos of numerous people in separate photos with Taylor Swift and how no one except Mueller had his hand by Swift's buttocks.More news: New 9/11 victim identified, almost 16 years later
Mueller testified on Tuesday and said that he might have touched Swift's "rib cage, or rib, or ribs", but did not grab her backside.
Swift's countersuit argues that the case will "serve as an example to other women who may resist publicly reliving similar outrageous and humiliating acts".
Mueller is seeking up to $3 million in damages.
About two dozen fans were in the courtroom, where Swift occasionally whispered to her mother and jotted down notes to her lawyers. Despite donating $250,000 to Kesha in 2016 for her own sexual assault legal battles, the "Tik-Tok" singer has been silent so far about Swift's case.
The trial is expected to last for 10 days. And her annoyance was evident when Mueller accused Swift's security of being disrespectful and dismissive to Melcher, and especially when he rationalized his deposition description of Swift as "cold and standoffish" by pointing out that she hadn't invited him into the picture with his girlfriend.More news: Knifeman arrested at Eiffel Tower `wanted to kill soldier`
During cross-examination, Swift's attorney, Doug Baldridge, noted that Mueller did not sue the radio station, and repeatedly said that "the jury will never know" what transpired during his meeting with his bosses, because of the destroyed recordings.
After the photo was taken, Taylor thanked them and she and Mueller shook hands, he testified. "Let's be clear from the start - inappropriate touching is wrong and offensive". Swift, however, did not specifically request that Mueller be fired. He also said it was an assault, not inappropriate touching. That's a possible reference to a photo showing David Mueller with his hand behind the popstar, just below her waist, before a 2013 concert in Denver. I know any Taylor Swift fact that you can ask me.
He also forced Mueller, who had been on the stand for more than 5 hours when this line of questioning came to be, to talk about how he felt Swift had been "cold and standoffish" toward him when he entered the photo room that day-June 2, 2013-something Baldridge pinned to Mueller having an ego as a local radio host.
Denver workers put up signs Tuesday in an office building across the street from the federal courthouse where Taylor Swift and David Mueller are standing trial.More news: No, the HBO Hack Wasn't Seven Times Bigger Than the Sony Hack