aka Skeleton Lake

Disturbed by his events in Nam; The Hunter (Hugh Lambe) seems to have become a crazed survivalist, who seems to believe said robbers and their captive have been sent to kill him. When a local comes to said captive's aid, he is slain by the hunter (presumably convinced the good Samaritan is in-cahoots with his potential hit squad). 

One of the surviving robbers joins forces with his captive in an attempt to kill the hunter. She is dispatched with a Vietnamese blade he obviously took as a trophy, while said robber sacrifices himself by destroying the tunnels in a failed attempt to bury the hunter.

Eventually, only the gang's leader is left, badly wounded. He is blown up in a truck with a small rocket launcher from the hunter in a sniper position. Despite his numerous injuries he sustained with the group, he limps over to the wreckage so he can use the flames to lit a cigar as he calmly observes his victim continue to burn.  

Thanks Nicholas!