A sign on the wall misspells the word "parafuso" by using an Z instead of an S.
On the kidnappers ransom note there's plenty of information on how to proceed and the amount of money asked but they never left any number for contact neither make mention of calling the family to provide more instructions. However, a few scenes later the chief of police and his detectives make two attempts to deliver the money - and at no moment the note mentioned a meeting place for such act.
The movie never presents any scene of the mechanic being questioned as suspect of kidnapping the boy. The chief of police goes to follow other suspects and it's never explained what happened with the mechanic.