It appears the stalker may have been killed by the Controller living in the cave. However the nature of the dialogue "Leave before is too late" or "Escape while you can" offers the possibility of a controller having living conditions, or even possibly a friend - the latter, though seems quite far-fetched.
Cause of deathEdit
Mirone is found in a fetal position, perhaps suffering from a fatal wound or attempting to shield himself from the controller's power. It's also possible, that the controller made the kill outside the cave and brought back the corpse to feed on it.
When found, Mirone usually has no loot but he might have a loaf of Bread or a Medkit with him. It should be noted that since his body will never disappear, it can be used as a stash of sort. Also, there are some various supplies mainly drugs and medical supplies scattered around the cavern, including a sample of the rare Anabiotics.
The easiest way of killing the controller is to toss some grenades deep into the cave. If it survives, take cover behind a bend in the tunnel then empty some bullets into its head. If one hasn't faced a controller before, this might be a good opportunity to practice combat skills against it.
Killing or leaving the controller makes no difference to the player.
Name Mirone strongly reassembles Latvian language word "mironis", which roughly translates as "dead man"