As the reader known, the Italians are so secretive that it is next to impossible to secure any information--even from the relatives of the murdered man.
The first thing is to locate the assassin.

An Italian detective is sent into the mine as a laborer.

Months may elapse before he gets on familiar or intimate terms with his fellows.

All the time he is listening and watching.

Presently he hears something that indicates that the murderer is communicating with one of his old friends either directly or through third parties.