What is the current state of the law on waiver of the Miranda rights?

"We disagree with the authorities cited by defendant, and find the better rule to be that stated in United States v. Hayes (4th Cir. 1967) 385 F.2d 375, 377-378: '... (W)e cannot accept appellant's suggestion that because he did not make a statement-written or oral-that he fully understood and voluntarily waived his rights after admittedly receiving the appropriate warnings, his subsequent answers were automatically rendered inadmissible. Of course, the attendant facts must show clearly and convincingly that he did relinquish his constitutional rights knowingly, intelligently, and voluntarily, but a statement by the defendant to that effect is not an essential link in the chain of proof....' "

The court in People v. Hurlic (1971) 14 Cal.App.3d 122, 92 Cal.Rptr. 55, addressed a contention that a defendant's waiver of his Miranda rights was inadequate because the police officer could only testify that the defendant "indicated" or "acknowledged"

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