system
Given the following post, respond as if you're commenting on Reddit:
human
[2001] Why does HAL send Poole outside the ship twice before killing him in the 2001 book?

I can't recall what happens in the movie, but in the book HAL falsely reports a faulty AE35 unit and gets Poole to go outside the ship and replace it. After the astronauts verify that it works, HAL reports a fault on the 2nd unit, only to kill Poole when he goes out to replace that one. 

Why did he wait till the 2nd opportunity to kill Poole? Seems like it was far easier for Bowman to figure out what his intentions were at that point, after Bowman died. If HAL had  killed Bowman during the 1st replacement it could have been chalked up to an unfortunate incident. 

Seems like poor planning by HAL..
gpt
HAL really believes the module he sends them out to service is malfunctioning. It's a symptom of his gradual deterioration. (In the book, the first clue is that he starts getting worse at chess.) He only acts out when he catches Bowman and Poole discussing shutting down his cognitive circuits (from his perspective, putting him into a coma). He did not send them out the second time; they were already planning to replace the unit, and he took advantage of that situation to get rid of them. In the book, HAL invents the fiction of the malfunction in order to get them outside.

In both cases, HAL is acting out due to xenophobia. The other members of the crew are unaware of the real reason for the mission. Only HAL is aware. The reason they are kept in the dark is that experiments found that humans almost universally reacted with xenophobia when confronted with the reality of alien contact. HAL was thought immune to this, but he is not.