vital evidence
vital information
vital clue

As such, it gives a vital clue to his thinking.

But you never know which pair of eyes or hands will find that vital clue.

Somewhere along the line we've missed out on a vital clue.

South was left to realize that he had missed a vital clue.

He had made the discovery that was to serve him as a vital clue.

The woman is believed to hold vital clues about what happened to Flight 858, officials said.

She had eyes everywhere, and they might notice a vital clue.

Like some vital clue telling her that the owner was home, after all?

The man got away but he may have left a vital clue.

"If she can't bother to return her own mother's calls, she'll have to get along without a vital clue."