A man was killed in his office. At the time of murder there were only four people in the office: Bill, Tom, Harry and Mike. When police interrogated them, they gave the following statements. Bill: "Tom did it." Tom: "Bill did it." Harry: "Tom's telling the truth." Mike: "Harry's not lying." After analysis, the police found out that only one person was telling the truth and the rest were lying. Can you analyse the statements and determine the killer?