In a city there are three types of people: "Cop", who always tells the truth, "Thief", who always tell lies, and "Spy", who tell alternate false and true statements. When interviewing three people from that city, you received the following statements:
Person 1: I am a cop.
Person 2: I am a thief.
Person 3: They are both lying, I am a spy
If there is a cop, thief and a spy among the three persons, which one is the thief?