Whether the key word to the situation is the phrase « Why didn’t they ask Evans? » or not doesn’t seem to me to matter much since you’ve no clue to who Evans is or as to what he was to have been asked. Let’s put it that the murderer or murderers assumed that Jones was in possession of some knowledge, whether he knew it himself or not, which was dangerous to them.
‘You see, you’ve asked the same question that Carstairs asked. Why didn’t they ask the parlourmaid? Why didn’t they ask Evans?’ ‘Ohi Bobby, we’re getting there at last » ‘The same thing must have struck Carstairs. He was nosing round, just as we were, looking for something fishy – and this point struck him just as it struck us. And, moreover, I believe he came to Wales for that reason.’
Why didn’t they ask Evans, Agatha Christie