It's clear that they indeed had more info from the Browns and Kato than they had indicated.
As Jasper notes in a recent post, their questions were very focused and were signed to lead O.J. to indicate motive, means, opportunity or to just catch him in a lie.
To be able to do that, they must've had rec'd more info from the Browns before the interview.
This also shows that O.J. was a suspect almost immediately after the murders.