Resolution:

A friend of mine has confessed to the "practical joke". Yes, it was a dumb mistake and he has apologized to myself and Warren profusely. He should have just called me immediately afterwards, but he hesitated or was preoccupied with other things.

I am glad that mystery is over, and I am happy that it was not someone who genuinely had a hate on for myself or Warren. It is too bad that it was a good friend though.