Whoever murdered Jansen was undoubtedly in Jansen' s office on the day of the murder, and both Samantha and Herbert were in Jansen' s office on that day  If Herbert had committed the murder, the police would have found either his fingerprints or his footprints at the scene of the crime  But if Samantha was the murderer, she would have avoided leaving behind footprints or fingerprints  The police found fingerprints but no footprints at the scene of the crime  Since the fingerprints were not Herbert' s, he is not the murderer
Thus Samantha must be the killer
No one but Herbert and Samantha was in Jansen's office on the day of the murder.