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I remember seeing this film as a kid which would make it mid 70's but the film may be older. The main hero of the film is one of three Aliens (good guys) sent to earth the track down and eliminate three bad guy aliens. Both sets of Aliens look Human until seen through special glasses, a bit like in "they live" but its not the same film. He is befriended by a girl and confides in her and together they track down the three bad Aliens only to be killed by a forth bad alien. The final scene shows the last remaining bad alien walking away with the camera view through the dead good aliens glasses.