FIRST STEP, inform police, or are you all going to be vigilantees.
These Ladies are as bad as anybody for not reporting their attack, as they are letting these guys go free to attack the next victim. Think on ladies, do you deserve our support if you are not prepared to start the ball rolling with the correct procedures, Go to the police.
Let the police go to the bar and interview these people. Other wise you are as bad as they are if YOU get the wrong person.
Baz