Regulus
Not the DMLE. There was a group called the Order of the Phoenix that helped, as well as a student group called the DA that was on the scene during the Battle of Hogwarts in 1998. That's when he died.
Voldemort never meant to make seven Horcruxes. It was purely accidental that the last one was made and he didn't know about it. He destroyed that one himself. But after the last of them was destroyed, he and I were in a duel. He cast the killing curse and I cast a disarming charm and because our wands were brother wands, both had phoenix tail core from the same phoenix, my spell overtook his and made his curse backfire, and killed him.