Is it true that the Criminal Investigation Brigade can check other people's phone records and text messages privately without the consent of its superiors?

Glad to answer for you!

Under normal circumstances, it is not necessary to bring a certificate to check, but if it is a difficult case or a special case, it must be approved by the sub-bureau at least before it can continue.

I hope my answer is helpful to the landlord. If there are any shortcomings, please ask me. If you are satisfied, please adopt it. Thank you.