Theresa Copeland was the mistress and colleague of Aaron Downing, as well as the accomplice of Aaron in embezzling from the insurance company that employed them, presumed by her to have been money they needed in order to run away together. She was also a suspect in the murder of Aaron's son Ryan, as he was injected with a volatile staph strain, and the needle used was outside her apartment building.
Theresa confessed to the embezzlement, but she denied guilt in Ryan's murder. Aaron himself was revealed to be the killer, motivated by depression projected onto Ryan. Theresa was imprisoned for her crimes, while Aaron jumped bail and committed suicide in a hotel room. (L&O: "Flight")