Interpol Wang returned to the bureau after the investigation of a killing scene. The old guard Zhang asked him how the result was, Wang said he knew the murderer had been there. Old Zhang knew that Wang Interpol was teasing him because Wang was not needed Tell him and he knows: If someone is a murderer, he must be on the scene when the crime occurs. But answering this, can we infer? ['If Zhang San was on the scene at the time of the crime, then he is a murderer.', 'If Li Si is not a murderer, he will not be on the scene at the time of the crime.', 'If Wang Wu was not present at the time of the crime, then he was not a murderer.', 'Even if Xu Liu is not at the scene, he may still be a murderer.']