Gang rape almost always leaves the victim with genital injuries and extensive bruising.
Exactly how are you an expert in this information? Watching Law and Order too much?
Sugar NF, Fine DN, Eckert LO. Physical injury after sexual assault: findings of a large case series. Am J Obstet Gynecol. 2004 Jan;190(1):71-6.
Of victims assaulted by more than one assailant, 38.9% did not have any evidence of bodily trauma (includes both genital and non-genital injuries).
If intellectual honesty truly matters to you, I suggest you revise your post.