When I picked it up (much to the amusement of my colleagues), I saw that it had been de-soldered off something, though none of the leads had been trimmed. Perhaps a hobbyist had used it in a prototype, decided to use something else, and then lost the loose part when he transported his project?
It turned out to be a BD902, a power transistor that can switch up to 100 Volts and 8 Ampère of current. Pretty hefty stuff!
Just what kind of hobby project would need such powerful transistors?