‘Why did HAL murder the crew?’ is one of the film’s big unanswered questions. Some believe the onboard HAL 9000 computer deliberately plotted to hijack the mission and its date with destiny. Others, quoting AC Clarke’s novel, say HAL was driven crazy by a programming Catch-22.
A simpler explanation: HAL screwed up. After he mistakenly diagnoses an antenna fault, the crew decide to disconnect his higher brain functions. From that point on, it is a life or death struggle for survival of the fittest. But that’s speculation: during filming, Kubrick drastically recast the ‘Jupiter Mission’ sequence, deleting any clear explanation of HAL’s behavior. It’s better that way.
Did you notice? After HAL’s error is discovered, Frank Poole tells Dave Bowman: ‘I’ve got a bad feeling about him’. It’s the film’s first reference to feelings. Facing a threat they only vaguely understand, the Earthmen regain that old ape intuition – and start to become human again.