The civil lawsuit centers on Swift's allegation that Mueller inappropriately touched her during a June 2013 meet-and-greet at Denver's Pepsi Center arena.
Mueller sued Swift, her mother and her radio promotions director in 2015 for $3 million in damages.
Mueller testified that he and Melcher were in the room with Swift and five other people: Swift, a photographer, a personal assistant, a tour manager, and a bodyguard.
"At nearly the same time that [Swift] said "Let's take a photo" or 'How about a photo, ' she put her right arm around Shannon [Melcher] and pulled her close, and the two of them turned toward the photographer, who was to Taylor's left and my left", he said.
"[Swift] put her right arm around Shannon, pulled her towards her, and turned toward the photographer", Mueller said. Swift's attorneys have pointed to that as evidence of the inappropriate touching, and noted that KYGO cited the photo as one reason for his termination. Mueller said: "I thought he was just telling me one of his stories".
When asked if there was any doubt her daughter could be lying, Andrea replied "None, never!" Andrea did, however, have Mueller escorted out of the building.
During her emotional testimony she gestured at Mueller and said, "He sexually assaulted her".
Andrea insisted she wasn't angry with Meuller, but more concerned for her daughter's well-being. I heard it directly from my daughter's mouth ... Taylor claims he lifted her skirt and grabbed her rear end.
Baldridge asked Mueller if Swift was the one who fired him. Out of a group of 60, eight jurors are to be selected for the trial. Today's court proceedings were delayed by a closed evidentiary hearing that lasted almost two hours.
Swift countersued Mueller, claiming sexual assault.
"What could happen to a young woman if she didn't have a companion to accompany her?" she said on the stand. The picture shows smiling faces of all of them and Mueller's right hand behind Swift.
Swift's attorney, Douglous Baldridge also shed light on Mueller's vacillating statements.
While David Mueller claims he was only touching Swift's ribcage with his closed fist while testifying on Tuesday, during cross-examination, the former KYGO morning show host admitted in the photo, his hand is clearly quite a bit below that.
On the other hand, Douglas Baldridge, Swift's attorney, accused Mr Mueller of having given seven accounts of the incident, while he also accused the DJ of destroying taped conversations with his bosses about the alleged crime.
"Let's be clear about something from the onset - inappropriate touching is offensive, it's wrong and should never be tolerated", Mueller's lawyer, Gabriel McFarland, told jurors.
Swift, who wore a black blazer, white blouse and had her hair pulled back, appeared fired up during her mom's testimony.
Taylor Swift shot daggers at a former deejay accused of groping her as he spent a second day on the stand struggling to shake off questions from her pit bull lawyer. "She's trying to tell people out there that you can say no when someone grabs you no matter who they are". "And that happens in our world", he testified previous year.
Andrea Swift said she knew if the allegations became public, the incident would dominate every interview Taylor Swift gave. "'There's a guy in the meet-and-greet".