Was checking the skyrail today and found two storage minecarts someone placed onto the racks. Chased them and destroyed both to keep the tracks clean.
But the problem is: they contained stuff like iron and gold blocks and even some diamonds. Did store all of it in a chest at my place.
Who did place those minecarts? And what the heck was she/he thinking to put valuables into unlocked storage carts?

When i found the carts they were already moving (just sitting in unloaded chunks) so i had to chase them for quite a bit. That's also why i destroyed them before someone not as nice finds them and thinks "easy loot". But i have no idea how to go on from here

Just wait for a about a week. if no-one comes forth saying its theirs then its yours to do as you wish