Man with a time machine who went back in time to find out who Jack the Ripper was.
A man grew up obsessed with the stories of Jack the Ripper. One day he obtained the use of a time machine for the purpose of uncovering the secret. When he got there, at the time and place where the first murder took place, the hour came and went. Then, he realized that HE was Jack the Ripper. In his madness, he used the time machine once more to enact the murders successfully. He performed every murder precisely as the legends dictated, down to the last detail.
And for those of you wondering about the paradox: In the original timeline, this same man had no outlet for his own tendencies (which resulted in his own obsession with his own crimes). Thus, since he existed around the same time that time travel was created (utilized, deemed safe, commercialized, whatever), he picked Victorian England as a target. That wasn't the only target originally; it's just that the other victims were somewhat less publicized due to the circumstances.
The particular form of time travel used has a built-in paradox prevention device, which creates an identical existence in the destination time frame while erasing the existence at the time of departure. In this way, alterations are minimized, and any actions that may prevent the existence of the individual in question do not remove their existence (i.e. the paradox example of killing one's mother (before one was born) via time travel).
