The sudden admittance was not something because of his guilty conscience, of course, it played a small part. But the most important thing regarding this feeling is actually Sam's killing intent.
It is his enormous killing intent and bloodlust that made them accept Sam's actions and take the pill.
The three of them are okay because they didn't really do anything they didn't care if they suffered some humiliation. It is better than Sam taking matters into his own hands. After all, they had seen the reports. Sam has killed so many people, that they didn't even dare imagine.
It is true that they waited for Sam's death under the Elite ten, but they didn't want to meddle and make an enemy out of him. After all, if he decided to flex his prowess a bit before dying, they would die too.
But the fourth guy tried to play it cool. Half of his mind said that Sam is bullshitting and there is no such thing as that pill. In fact, his mind was right.
