The different semen in case of gang rape is identified by:-
Acid phosphatase test
Christmas tree stain
PSA
Single photon flourimetry
Single photon fluorimetry has been used to differentiate between different semen in a gang rape case TESTS FOR SEMINAL STAINS Creatine phosphokinase test Acid phosphatase testQ Florence testQ (Choline iodide crystals) Barberio's test (crystals of spermin picrate)
Trace evidences