can an iPhone be released from iCloud activation without the previous owner

No. If you purchased a used iPhone, which is activation locked, the only person who can unlock it is the person who locked the phone. If you don't know them or can't reach them, the phone is 100% useless to you. Apple will NOT help you. We cannot help you. If you can't get whoever locked the phone to unlock it, or if you purchased it and can't get a refund, recycle the phone responsibly.

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If you are not the original owner, the phone is Activation Locked, and you do not have the credentials to unlock it, Apple will not help you.

(*) If the phone belonged to someone who died, and you have the official certificate and official court orders granting you the right to administer their estate, then Apple might help you. But that is a very special case.