Transcript for Taylor Swift expected to take stand as trial begins over DJ groping claims
We move to that Carter battle for Taylor Swift getting ready to take the tan in her suit against a radio deejay who she accuses of groping her during a photo-op. This photograph will be a key piece of evidence in the trial. He's suing her, as well and ABC's Clayton Sandell is at the white house in Denver where it all began. That's where it will begin today, Clayton. Good morning. Reporter: Good morning, George. It is the hottest ticket in town and soon Taylor Swift fans will be lining up in front of the courthouse here hoping to catch a glimpse of the superstar as she begins her courtroom showdown. ??? Bad blood ??? Reporter: This morning, bad blood between a pop star and former radio deejay now suing each other in federal court. ??? Reporter: It all goes back to Denver in 2013, this photo a key piece of evidence showing Taylor Swift backstage before her concert posing with deejay David Mueller and his then girlfriend. Swift claimed Mueller's hand grabbed her back side inappropriately and his radio station fired him suing for potentially $3 million in damages. ??? Trouble trouble trouble ??? Reporter: But swift counter sued for assault and battery claiming Mueller took his hand and put it up my dress adding it was not an an accident and says it caused her extreme anxiety. But Mueller says that's not the case. In court documents and a radio invupts saying there was no inappropriate contact of any kind. My hand was never under her skirt. I never grabbed her. Reporter: Now it's a legal he said/she said. Swift's camp said the singer complained to her "The afterlove" it while Mueller said he asked her security team to call the police. I didn't do anything. Last month a judge sanctioned Mueller for losing or destroying four devices including a laptop and iPad that held copies of a conversation Mueller secretly recorded with his boss the day before he was fired. That boss has alleged Mueller may have changed his story. Swift is expected to take the stand saying in court documents she wants to hold Mueller responsible and to serve as an example to other women in similar situations. One hurdle for Taylor Swift will be her lack of reporting to police. Especially given the fact that she is now claiming that the reason why she is counter suing is because she wishes to advocate on behalf of women and victims. Taylor Swift has said if she does receive any monetary claims from this case, she will take those moneys and donate it to causes that advocate on behalf of women and victims. Reporter: Now this trial is open to the public but there are only 32 seats available every day and the court is already warning fans to leave those Taylor Swift t-shirts at home telling them this is a trial, not a concert. George. See if they listen. Okay, thank you. Let's talk to Dan Abrams for more on all this. We got dueling lawsuits right here. Boy, but it doesn't look good for the deejay to have destroyed all those devices. I see a lot of problems for hip. Number one is the fact that he's been sanctioned by the court for destroying or losing an audiotape that he made of his conversation with his boss right before he gets fired. He spilled coffee on his computer then I threw away my phone and lost my iPad. All these different things as to what happened to that critical piece of evidence in this case. Number two is the picture itself. I mean his side is saying this helps us. I don't know how -- look where his hand is. It's an odd spot for your hand to be when you're taking a picture with a celebrity that you don't know. Is it dispositive, will ite or break the case, no, but I don't know that it helps. Number three the law. 'Basically claiming that she is the reason he got fired. You have to show intentional conduct on her part and number four is why of all the people in the world does she decide to make up a story about this guy? Right? I mean she just decides out of whole cloth -- you know what, I'm going to invent a story about this Denver deejay, so there are a lot of problems, I think, for him. He has a lot of problems. What about her suit. Look, I think the biggest issue for her and you heard ha in the piece is the fact she didn't report it to the police immediately. You can say, look, you're Taylor Swift. You have some guy who, you know, grabs your tushie and says, I'll let this go. I'm not going to call the police about it and she probably minimized it at the time but the bottom line is once she got involved in the lawsuit she said, I was assaulted in the context of this. This wasn't as minor maybe as I initially made it out to be and as a result she then reports it. I don't see it being that big a deal. The key thing how she will do on the witness stand. Thanks very much.
This transcript has been automatically generated and may not be 100% accurate.