Jim Preston is a transgender soldier who witnessed the beating and rape of Sandy Ksenivch.
Preston decided to enlist while still in college and hid the fact that he was born female from those he served with. As a result, out of fear of outing himself in the process, Preston initially refused to help the detectives in their investigation, going so far as to repeat his name and rank over and over.
When the case was brought to trial, Preston was too afraid to testify, knowing that the military wouldn't allow transgender people to serve. Eventually, he changed his mind, and when the defense counsel questioned him, he came out as transgender. After the trial concluded, all those in the military saluted him. (SVU: "Service")