A compromise here is not technically possible. There is no half crypto. Crypto with a backdoor is not crypto.

Someone's encrypted files should be regarded to be in the same category as material they memorized in their brain. Off limits.

Find some other way to get evidence about their wrongdoing to convict them.

In a situation where an accused criminal used Whatsapp and decrypting it is needed to view the content which may or not lead to a conviction. This ridiculous idea that law enforcement knows people are guilty and it is these pesky rights that keep getting in the way is just false. Police regularly and consistently abuse their power to railroad people and take the easiest path to convicting someone.

Even in situations where citizen rights do “get in the way” of convicting the guilt, that is the price we pay to not be thrown in jail for crimes we didn’t commit. Former Supreme Court Justice William O. Douglas said “It is better, so the Fourth Amendment teaches us, that the guilty sometimes go free than the citizens be subject to easy arrest.” He also said “Big Brother in the form of an increasingly powerful government and in an increasingly powerful private sector will pile the records high with reasons why privacy should give way to national security, to law and order... and the like.”