for plain, but facts aware person:
- think CyberCaffe
- think dinamic IPs
for a more seasoned person:
- think mysql and (id_char_from, id_char_to, id_item, timestamp)
- think SELECT u.name FROM users as u, trans as t WHERE u.id=t.id_char_to AND t.id_char_from='NAME_OF_ROBOT'; this way you can trace any transaction to any player using TRADE functionality. this can be done in levels, automated, only input needed is the original sinner.
HINT: drop items on floor ;p
naturally, if you trace all items char NAME_OF_ROBOT had and check who has those items now... then even dropping won't help