Accidentally indecent expose at workplace?

How do you weight the words against words where a woman saw a guy in in a boys toilet when she walk in? This has become a police case and they took down the statement from a guy to explain but the officer said he doesn't find it convince to his side story. If there is no evidence to proof that the guy has intention to expose to the woman or couldn't find any witness from both side, will the prosecutor still bring this to trial? Giving percentage, how do you think the guy will win the case using English Law.