Because there are a few things which happened that no-one else knew about as it was privately arranged.
Kaito spent the entire day tending the Jester's wounds. He also chained up the black leopards in the Jungle Bedroom with some of the bondage gear from the Gem Bedroom before trying to unlock the door they guarded. That's why they attack him now. (He did not get the door open, he was caught straightaway.)
(For the record, the corner of one of the fields in the yard was dug up on Day 8. The items buried there were taken by Kaito.)
Murtagh was in his cell all day.
Mukuro got attacked by the garden during chores so anyone working that may have glimpsed him injured at the time before he covered it with his own illusions.
What Happened the Past Week... (Mukuro/Murtagh/Kaito only)
Kaito spent the entire day tending the Jester's wounds. He also chained up the black leopards in the Jungle Bedroom with some of the bondage gear from the Gem Bedroom before trying to unlock the door they guarded. That's why they attack him now. (He did not get the door open, he was caught straightaway.)
(For the record, the corner of one of the fields in the yard was dug up on Day 8. The items buried there were taken by Kaito.)
Murtagh was in his cell all day.
Mukuro got attacked by the garden during chores so anyone working that may have glimpsed him injured at the time before he covered it with his own illusions.