Monster a-Go Go
The plot concerns an American astronaut, Frank Douglas, who mysteriously disappears from his spacecraft as it parachutes to Earth. The vanished astronaut is apparently replaced by or turned into a large, radioactive, humanoid monster. A team of scientists and military men attempt to capture the monster — and at one point succeed, only to have him escape again. Neither the capture nor the escape are ever shown, simply mentioned by the narrator.
Starring
Watch "Monster a-Go Go" on shudder-shudder-subscription released in 1965. It's a science-fiction and horror movie, and has a rating of 1.7 out of 10 from Imdb which is fairly low for this kind of movie.