I like this film a lot. It's very much a 60s crime film... slow, twisty, existential, complete with nihilistic ending. I agree that it would be great to see an English version of this - I've got an old German VHS, but that's it (and I'm pretty sure that doesn't have Linda Sini in it either)
Guerrini also made Date for a Murder, which is also pretty good, before drifting into comedies in the 70s. Has anybody ever seen his Colpo del sole? It's one I've never been able to track down a copy of and it sounds interesting...