Mr Forleo is accused of firing the shot that killed Vito Ferrarese, a small-time bandit, during a police sea chase in July 1995. He is also accused of having approved a police cover-up and of later putting pressure on his colleagues not to incriminate him.
When told of his imminent arrest, Mr Forleo, 57, tendered his resignation before being transferred to a jail in Rome.
The arrest of one of the country's most prominent police officers has been greeted with incredulity among the police and by politicians who knew him during his brief spell as a parliamentary deputy. It follows a continuing investigation into the activities of the special "capture" squad in Brindisi during the early Eighties.
Five members of the squad, including several senior officers, were arrested in March. They were accused of staging police raids with the complicity of the local Mafia group, the Sacra Corona Unita, to obtain promotions and of favouring some clans. The inquiries have revealed a "wild west" regime in which any means appears to have been justified in the battle against the local Mafia andcriminal gangs trafficking in arms, drugs, cigarettes and illegal immigrants.
After many interrogations, some of the arrested policemen began to confess and point the finger at fellow officers.
The magistrates subsequently reopened the file on the shooting of Ferrarese, whichhad been quickly closed despite a report by the coroner that the bullet that killed him did not correspond to the pistol listed in the official police report.
The events of the night of 13 July 1995, during which Ferrarese lost his life, have been pieced together by some of the "capture" squad who were on board a helicopter.
In a statement to magistrates, leaked to La Repubblica newspaper, Giorgio Oliva, head of the squad, recounted that the helicopter had chased a known smugglers' craft, and that Mr Forleo and others had fired shots and thrown hand grenades to force it to halt.
Mr Oliva said that when they landed and found the boat with Ferrarese dead inside, they procured a machinegun and placed it on board, to back up the police line that they were being fired at by the bandits. He added that when the coroner ascertained that the fatal bullet was not fired from the gun listed in the police report, he was asked to take the blame, saying he had fired Mr Forleo's pistol.
According to magistrates in the southern Adriatic port of Lecce, Mr Forleo had until just a few days ago tried to convince fellow police officers at the time not to incriminate him.