Jim "J.T." Thomasen first appeared in flashbacks and memories of Laura Kirk English. J.T. was a man who agreed to take pornographic pictures of her so she could make money to help her sick mother. Laura and her boyfriend Scott Chandler, ventured to New York City in order for Laura to put the past behind her. Jim Thomasen spotted her and found out that she was being adopted by a wealthy woman, Brooke English. Laura and Scott returned to Pine Valley. A short time later, Brooke had an awards ceremony in New York and wanted Laura to accompany her. Laura agreed. While visiting for the second time, she ran into Jim. Jim confronted her and told her that he knew one of her dark secrets. Jim told her that he saw her burn her pornographic pictures in the basement of her SRO apartment building. That night a fire erupted in the building and, unable to escape, claimed Laura's mother's life. Laura left New York and ran back to Pine Valley. Brooke wanted to return to Pine Valley to be with Laura, so she swapped her ticket with Janet Green so that she could get on an earlier flight. Jim followed. Tragedy struck as the plane Brooke was flying in exploded and crashed, killing all but four passengers - Jim, Brooke, Edmund, and baby Maddie. Jim played the hero by helping Brooke save Edmund and Maddie, but did not save Maria in time. Maria went into the waters below.
Brooke looked to Jim for comfort, which he was happy to oblige. Jim and Brooke became very close during the first investigation of the crash. The crash findings showed that Adam Chandler, owner of the airline, purchased faulty remanufactured turbine blades. Jim continued to blackmail Laura into keeping quiet about the pictures he took of her back in New York. Jim then conspired with Ricky, a drug addict who was photographed with Laura, to kidnap her. Laura's pictures showed up on the internet and were plastered all over Pine Valley. Jim told Laura that she might be better off in Boston, a city where nobody knows who she is. She could make a new start and live happily. Laura agreed and left for Boston. Jim meanwhile asked Brooke to marry him, she never answered.
Brooke got word that after investigating the crash site for the second time, they came up with a piece of luggage that carried explosives on board Flight 149. She ran and told Jim. Together they looked at the luggage fragment. Jim acted peculiarly and shied away from any talk about the fragment. He urged Brooke to put the past behind her. Brooke would not let it rest and one evening in Jim's room found a piece of luggage that matched the piece found at the crash site. Brooke became leery of Jim and confronted him with her findings. Jim made up several stories about how the bomb had made its way onto the plane. He eventually settled on a story where a loan shark had planted the bomb in his baggage to kill him off for not repaying a debt. Brooke told him that she believed him, but she really didn't. She notified Mateo Santos and asked him to uncover anything he could about Jim Thomasen and the crash of Transglobal Flight #149.