mesmerizing

Yes!!! Agreed. 

"Few people know this yet everyone knows Fellini." Yes? Fellini is a master of cinema. Petri is sort of like Costa Gavras with black humor. Solid ideas/intent and strong thriller mechanics, but little in the way of poetry. But the dialogue is often excellent, as is Volonte's performance, if a little one note. The film is best in its description of police methodology rather than its thin psychological underpinnings, however vogue they were amongst leftists at the time. Watch Marco Belocchio's Leap into the Void for a less ideologically motivated and richer take on similar subject matter.