But he was released when authorities could not establish proof.

In this case, establishing such proof could be challenging.

Still, prosecutors are not historians; their focus is on establishing proof.

The Shadow had let crime start, to establish proof of the crime ring's methods.

For centuries historians have attempted to establish some factual truth or proof of the event, without success.

The request established "concrete" proof, the agency said, of the government's willingness to hand over indicted war crimes suspects.

Bolan did not need to establish legal proof, nor was he interested in political influence.

Nevertheless, the good clinical results in the first patient established "proof of principle".

What researchers need in order to establish proof is a double-blind controlled clinical trial.

In such circumstances should an extensive procedure be undertaken to establish proof?