An attorney for Dr. David Dao, the passenger who was forcibly removed from a United Airlines flight Sunday, warned of a likely lawsuit against the company Thursday as he condemned the airline for using “unreasonable force and violence” to remove Dao. Crystal Dao Pepper, one of Dao’s daughters, said her family was “horrified” to see her 69-year-old father on video being violently dragged out of his seat and down the aisle of a United Airlines flight after he refused to give up his seat to a United crew member. “It has been a very difficult time for our entire family, especially my dad,” she said at a news conference with his lawyers. “What happened to my dad should have never happened to any human being regardless of the circumstance. We were horrified and shocked and sickened to learn what had happened to him and see what had happened to him. We hope that in the future nothing like this happens again.” “Seeing it on video made those emotions exacerbated,” she added.