Italy's Supreme Court has cleared three men who had been sentenced to life for a bombing seen as one of the worst post-war terror attacks in the country.
Seventeen people died in the blast at a Milan bank in 1969.
The court upheld a decision by a lower court last year to quash the convictions of three former members of a neo-fascist group.
A lawyer for families of the victims said that his clients were "disgusted" by Tuesday's ruling.
"This is another piece of our history that is shrouded in mystery," Federico Sinicato told journalists.
One of the former defendants, Carlo Maria Maggi, said he planned to celebrate the verdict.
A fourth man convicted of being an accessory to the crime had his one-year sentence overturned, Reuters news agency reports.
The bombings in Milan's Piazza Fontana marked the start of more than a decade of violence between extreme political groups.
The blast remains unsolved.