Why can't I loot Dr. Mercy's body?

I was doing the Medical Mystery quest from Dr. Zed to investigate a new type of weapon being used, and it involved finding, killing and then looting Dr. Mercy. However, when I get to the part where I'm supposed to loot Dr. Mercy's body, it won't let me interact with his body to loot it. The quest marker shows a spot to go near the entrance of the cave (i.e., not where his body is), but there's nothing there, either.

How can I loot him to complete the quest?

Solution 1:

Apparently this is a glitch that often occurs if you kite Dr. Mercy and kill him outside of his cave. His corpse becomes unlootable and the quest marker gets very confused.

To fix it, leave the Three Horns Valley zone and then come back. Head back into his cave and you should find his body right on that stairway he first appeared on (NOT where you previously killed him). You should now be able to loot his body to find the mysterious weapon.

Solution 2:

I had this same issue when I killed the Doctor next to the electrical pillar, it was also showing the location in an unreachable part of the cave. I never left the cave, nor did the doctor, but I did die, and killed him during my second chance period. I noticed there was a series of corrosive, slag, and explosive barrels behind the metal paneling lining the area I could not reach, it seems like the area has several glitch issues. Leaving the area and coming back made the Doctor's body respawn at his original spawn point, and I was able to loot the corpse.