who left kreacher on an island
Kreacher travelled with Voldemort to the cave and inside, Kreacher was made to drink all of the potion so Voldemort could see the effects his enchantment would have on any thieves. Voldemort then left Kreacher on the island to be killed by the Inferi in the lake. However he forgot that house elves could apparate and disapparate within the cave and Kreacher was able to return home and tell his master, Regulus, what had happened.