[cantbebought]

The first part of A Knife in the Dark is 3 of the Nazgul breaking into the house at Crickhollow....Run, Fatty, Run...but has no details on the Prancing Pony attack.
It could have been the Nazgul, but Strider tells the Hobbits:

..."But thier power is in terror, and already some in Bree are in their clutch. They will drive these wretches to some evil work: Feerny, and some of the starngers, and, maybe the gatekeeper too. They had words with Harry at West-gate on Monday. I was watching them. He was white and shaking when they left."

So that's why I suspected the others but it could be either way.

[HairOfTheDog]

I think it is quite plausible... And you are right, at least three of the Nazgul have an alibi for that night!

[LinnieBeth]

"But thier power is in terror, and already some in Bree are in their clutch. They will drive these wretches to some evil work: Feerny, and some of the starngers, and, maybe the gatekeeper too. They had words with Harry at West-gate on Monday. I was watching them. He was white and shaking when they left."So that's why I suspected the others but it could be either way.

Hmmm, I didn't even remember this conversation, think you are probably right!