Umberto Lenzi was a man of all genres, chasing whatever area of exploitation cinema happened to be popular at the time in Italy. He is probably most famous (and infamous) abroad for starting the whole cycle of Italian pseudo-ethnographic cannibal films with 1972’s Man from Deep River, which he followed with Eaten Alive! and the notorious Cannibal Ferox, but he also made erotic thrillers, gialli, spy movies, war films, horror, oaters and poliziotteschi.

His versatility in genre is advertised (and satirised) in Free Hand for a Tough Cop. For while its title accurately suggests a poliziottesco, it opens with five cowboys riding through a desert locale reminiscent of Monument Valley, as though we were instead watching another of Lenzi’s Spaghetti westerns (like Pistol for a Hundred Coffins or All Out).

This western is, in fact, a film-within-a-film, being watched by a group of prison inmates – although not before the title has appeared on screen, as though part of the western. It is almost as though Lenzi is suggesting that his brand of masculine action narrative transcends genre, and could equally be told as oater, crime thriller or even war movie (later, during a shootout, one character will expressly compare the other side’s heavy ordnance to the The Guns of Navarone).

Among the prisoners watching the western is Sergio Marazzi (Tomas Milian), whose nickname “Monnezza” (“Garbage”) clearly signifies his lowlife status. So beloved with viewers would this sleazeball character prove that he would return in Lenzi’s Brothers Till We Die – where Milian also reprised his role as Monnezza’s brother Vincenzo Marazzi, whom he has previously played in Rome Armed to the Teeth – and in Stelvio Massi’s Destruction Force.

After falsely framing the beginning of his film as a western, Lenzi wrong-foots the viewer again, as he shows Monnezza being knocked unconscious and broken out of prison, only for the con’s attacker/liberator to be revealed as hard-boiled police commissioner Antonio Sarti (Claudio Cassinell), the ‘tough cop’ of the English title, desperate to exploit Monnezza’s underworld connections to solve a case. Antonio is racing to track down little Camilla (Susanna Melandri), whose kidnappers have a habit of murdering their captives, and who will in any case die within days if she does not get medical attention for her kidney disease. The clock is ticking.

“I’m just a cop,” declares Antonio, to which Monnezza replies, “Yeah, and I’m a bum, that makes us the odd couple.” Sure enough, Lenzi pairs this tough-as-nails police detective with a lovably scuzzy new criminal partner for some violent buddy comedy, some six years before Walter Hill would use a similar premise for 48 Hrs. The pair has soon recruited a trio of ruthless train robbers (Robert Hundar, Biagio Pelligra and Giuseppe Castellano) to join them on the hunt for the kidnappers, and begin aggressively shaking down Rome’s criminal fraternity for clues to the gang’s whereabouts.

What ensues is a series of inversions. Antonio, who is already under a cloud for not playing by the rules and makes repeated references to the fact that he was transferred for a time to Sardinia as punishment for misconduct, finds himself increasingly compromised by the trail of corpses left by his new criminal colleagues.

Monnezza is a snivelling, whining, wheedling, witty, weirdly fatalistic con artist and master of disguise whose “heart of gold” quickly draws him to the cause of rescuing Camilla, even if we are never allowed to forget that he is also an utterly ruthless murderer (and, at least by implication, a sheep shagger). Antonio’s other three foot soldiers are initially motivated by a personal (and falsely premised) vendetta against the chief kidnapper Brescianelli (Henry Silva), although the aims and intentions of this rape- and-trigger-happy trio become more complicated and varied as the film goes on.

As Monnezza plays trickster Odysseus to Antonio’s more strait-laced Achilles, Free Hand for a Tough Cop tests out different modes of heroism, while having fun mixing and matching these two characters’ key traits in their improbable but effective partnership. Meanwhile the action never stops, with endless car chases, gun battles, heists and hits all marking ’70s Italy as the most dangerous place on Earth.

The results are vicious, visceral and funny, utterly cynical and yet somehow sweet to boot. Along the way, practically every prominent poliziotteschi actor of the day gets a cameo as a rogues’ gallery of ruffians and robbers gets in the way of an innocent, ailing girl’s future. Camilla may as well have been called Roma…

Free Hand for a Tough Cop is released on Blu-ray from 29 November via Fractured Visions.