A Plot Hole

So recently I read the books over again, and I realised a pretty big plot hole: The Capitol had Katniss and Peeta at their mercy for a whole week after the Games finished. So why didn't it kill them then?

If they killed Peeta:

This wouldn't be that suspicious- he was practically dying in the arena anyway. They could say it was an accident and that it was his leg that liked him. Even if the Districts did suspect, or would send the right message, that anyone who rebelled would be killed.

If they killed Katniss:

This would be more suspicious, but it could be ed of as consuming too much of the nightlock or something like that. This would send more of a message to the rebels, and this would probably be the better option for the Capitol as they would then have complient and non-rebellious Peeta.