Shouldn't Dumbledore have known that Sirius helped Voldemort find the Potters?

In Chapter 1 of Philosopher’s Stone, Hagrid mentioned that Sirius Black lent him his motorbike. Based on the information we now know from the earlier parts of Prisoner of Azkaban, Dumbledore was still under the impression that Sirius was STILL the Potters' Secret-Keeper. It was only in the ending of this book that we found out that the Potters' Secret-Keeper was switched from Sirius to Wormtail. We eventually find out that Voldemort got to the Potters' on Wormtail's information.

Since Dumbledore was still under the impression that Sirius was the Secret-Keeper (a fact to which he himself gave testimony to the Wizarding body) shouldn't he have immediately blame Sirius for the Potters' death? After all, Voldemort could have only known their location with the help of Sirius. (Again, we know that this was not the case, but on October 31-November 1 that was still the only information Dumbledore had). See where I am getting to, or have I lost you?

Anyway, Hagrid mentioned again that he was going to return the motorcycle to Sirius after he dropped baby Harry off at the Dursley's, yet Dumbledore did not do anything to stop him.

Don't you think Dumbledore should have warned Hagrid and alerted the Ministry of Magic about Sirius as the betrayer of the Potters? Do you think this is just a result of JK Rowling not knowing that she'll use Sirius in future books?