The Plot Thickens

Based on the investigator's analyses, the culprit's motive and methods were already revealed, becoming clearer by the minute. The case went something like this: before the robbers robbed the bank, they already registered one more different safety deposit boxes.

When they actually robbed the bank, they opened their own as well as seventeen other boxes. Actually, out of the seventeen security boxes, there was only one or two that contained their true target! In order to throw the police off track, after breaking into the boxes with the desired possessions, they also destroyed the contents of the other boxes, scattering them all around.

Then they put the item they planned on stealing into the safety box under their own name, then left the bank empty handed. A day later, they returned, and using the bank's confirmation method, took the item under their own name and left!