Biagi was assassinated by the extreme-left Red Brigades as he made his way home in March 2012, shortly after Scajola, who was interior minister at the time, had taken away his police escort.
Prosecutors are now looking into whether Scajola, currently in jail for allegedly helping a Calabrian businessman escape a five-year-jail term for a mafia collusion conviction, and other officials are guilty of murder by omission after failing to do what they could to prevent the killing.
During the mafia-related probe, police found a note written to Scajola, warning him that Biaggi, who was 51 when he died, was in danger.
Maroni, who was welfare minister at the time, admitted on Thursday that it was him who wrote the note because he was “afraid for Mario’s life”, TGCOM reported.
“It was me who wrote the letter to the interior minister Claudio Scajola. I asked for Marco Biagi to be escorted, and in Bologna, where he lived,” he was quoted by the news site as saying.
But the request for police security was never taken up.
In a letter to Maroni, Biagi wrote that he had repeatedly told police about receiving threatening phone calls, but that no action was taken.
Scajola was forced to resign as interior minister in July 2002 after being caught in a wire-tap vilifying Biagi.
Scajola, who also served as industry minister under Silvio Berlusconi’s government, has long been dogged by scandals.
He was forced to resign again in 2010 over allegations that he bought a luxury flat next to Rome's Colosseum with bribes but was later cleared after claiming he did not know it was being paid for by someone else.