In one of my old forts a trading caravan arrived on the opposite side of the river across from the fortress. They decided to cross the river near the edge of the map where the water flow was lower then the rest. As soon as they stepped in to the river they were doomed, they weren't able to get out. At some points the trader or the Oxen would step out but for some reason they would immediately move back in to the river and become trapped again.
All of this was happening late fall, and I was curious as to what would happen as soon as it was enter and all the ice would freeze. When the ice formed all the traders instantly perished. I suddenly realized, this means I get free stuff! So I immediately told my Dwarves to go and channel into the ice to gain access to the goods. As soon as they dug down I found the corpses and the goods. Heres the weird thing, all of the corpses were actually skeletons. Weirded out I moved on and set the goods so that they could be gathered and moved back to the fortress. About 20 minutes(real time) after I took the goods, the traders and guards rose as ghosts and started to haunt my trading depot. They stayed there until my fortress failed, approximately 5 minutes later when a failed attempt at created a well caused the mines and then the fort to flood. Sadly I didn't notice until I was spammed with messages of "Urist Mcsomething canceled store item, could not find route." turns out he was trapped and drowned shortly. I tried to salvage the fortress but my attempts were crushed by a group of goblin ambushers...