First of all, it will depend if they used a condom or not.
Second, It will depend whether the victim is male or female. The risk is higher if he is male and lower if the victim is female.
Also it will depend wether there was direct blood contact between the two or not during the intercourse?
And last but not least, what kind of sex was that. Anal, oral, homosexual or normal? The higher chance to get HIV is between anal sex, because human anus doesnt produce mucus/fluid to allow penis to enter (thee fluids act like "grisi" or lubricants in machines. They reduce friction). Hence chances of blood contact is high.