There would be many things that would have been missed out on as a result of them not closing down the crime scene right at the moment when they arrived, and could have realised that it was murder rather than being an accident or a suicide.
It was possible that even if everything went like Ash wanted it to, there would be some suspicions left over toward who was using the rooms on each side of the room that belonged to Jack.
Having those two people not show up during a time when there would be a need to question them to find out if they happened to hear anything would make it difficult for them to learn anything, and it would make them slightly suspicious of those two people.
Even if Ash happened to be successful during the initial stages of the investigation and threw off the investigation a little, she had to be prepared to throw away those two forms, as they could end up becoming potential suspects.
