Movies Like 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.