|Spoiler Inside: Solution to Puzzle||SelectShow>|
Assume B2. Then D1 and D2. By D2, Al did it. Therefore, B1. However, this means that Bo and Di both told the truth both times. This is a contradiction.
Therefore, not B2. Assume C1. Then, not B1. Therefore, Bo or Di did it. Therefore, A1 and not D2. Di could not have lied both times so D1 and so Bo did it. Therefore, not A2 and C2. This is consistent.
Assume the last assumption was wrong (to check for other possibilities): not C1. Therefore, B1 and Al or Ci did it. Therefore, not A2, C2, and D1. Both fencesitter positions are taken so not A1 and D2 and Al did it. This is consistent.
This means that either Al or Bo did it, and that is all we can tell.