Italian prosecutors have released a video of a mafia-style murder in Naples met with indifference by bystanders, hoping it would help break a wall of silence over the identity of the killer.

The video, shot by closed-circuit cameras, shows a man wearing a baseball cap shooting dead Mariano Bacio Tarracino, a 53-year-old man with a mafia criminal record, in broad daylight on May 11 this year.

Mr Tarracino is seen smoking a cigarette outside a bar in the central Sanita neighbourhood. The killer enters the bar, where there are at least six people, then emerges and shoots Mr Tarracino at point blank range. When Mr Tarracino falls on the ground, the killer finishes him off with a bullet to the head.

None of the bystanders moves a finger, although it is hard to say if that is from genuine indifference or fear of retaliation.

A woman is seen rubbing off her scratch-and-win lottery card as Mr Tarracino is killed in front of her. A cigarette-seller moves his stall a few metres down the road, while a man holding a toddler in his arms looks at the victim and walks away.

After five months of investigations, prosecutors have yet to identify the killer, despite the fact that his face is clearly visible in the footage.

"We have decided to circulate the video as widely as possible, urging the cooperation of whoever can provide information to identify the killer and his lookout," the Naples' office for anti-mafia investigations said in a statement.

The video, top news on the websites of leading Italian media, prompted outrage from politicians. A member of the Green party in the Campania region around Naples offered €2,000 for information leading to the killer's arrest.

Naples, Italy's third biggest city, is home to the Camorra crime syndicate and its residents have become inured and all but resigned to the almost daily violence on its streets.