Based on the research I just did, I believe it was manufactured by ASM (Armi san Marco). Consensus is that only 2 companies made these. Pietta and ASM. The barrel is stamped with "Made in Italy" but I don't see any Pietta related markings on the underside. There is what I appears to be a AM mark so I'm assuming that's what it stands for.

I"m secondhand owner on this pistol so I don't have the original packaging.

I hope that's helpful.