Kevin Kimmel was in a petrol station in New Kent, Virginia when he noticed a "kind of unusual" RV nearby.
"The thing that stuck out was that this was an old RV with black curtains which wasn't very family-ish," he said.
Moments later he saw a man enter the vehicle and it began to rock back and forth. Kimmel says he saw a "minor female" behind the curtain and called 911.
Police arrived at the scene within minutes and rescued the 20-year-old woman, who had been kidnapped and used for sex trafficking.
Iowa couple Laura Sorenson and Aldair Hodza were sentenced to 40 and 42 years in prison for kidnapping the victim, torturing her and forcing her into prostitution.