If Sirius is innocent, and Dumbledore knew it but couldn’t prove it, then the swap could have been done by Dumbledore, replacing some other Deatheater (not necessarily Peter) with him.
Goblet of Fire (and Barty Crouch Jr’s escape after swapping with his mother) shows us that Dementors are okay with you bringing in a fresh victim to trade for a less fresh one.
That would be possible, but doesn’t match the hints. Sirius would have been in Askaban, it wouldn’t explain the confrontation, and the scene with Fawkes would be out of place if Dumbledore knew.
If Sirius is innocent, and Dumbledore knew it but couldn’t prove it, then the swap could have been done by Dumbledore, replacing some other Deatheater (not necessarily Peter) with him.
Goblet of Fire (and Barty Crouch Jr’s escape after swapping with his mother) shows us that Dementors are okay with you bringing in a fresh victim to trade for a less fresh one.
That would be possible, but doesn’t match the hints. Sirius would have been in Askaban, it wouldn’t explain the confrontation, and the scene with Fawkes would be out of place if Dumbledore knew.