The film was shot in English and then dubbed into Italian.
I don't understand that especially as most of the cast were Italian and were being asked to speak in English, perhaps even phonetically with their voices being dubbed by English speaking actors to hide the Italian accents.
The Italian language version is better although it's always given me the impression that Terence Stamp had no idea what was going on.

IMDb has a credit for dubbing for Stamp's role by
Pino Colizzi
. I can only assume this is correct.
Peter