Actually only Mussolini and his mistress Clara Petacci were executed outside an farm house in Mezzegra, where they were being held.
The secretary of the Communist Party ordered that 15 Fascists be executed. So, the 15 were selected from where they were held captive. They were brought to the square at Dongo and lined up and executed. Clara Petacci's brother, Marcello, tried to escape by jumping into the lake and was shot.
The bodies were taken to Milan for public display. Archille Starace(Secretary of Fascist Party 1931-1939) was arrested and executed on the spot.
Most of the 15 Fascists were no longer serving in any current position with Mussolini. One was Capitano Pietro Calistri, who was innocent of any connections to Mussolini or his staff.