Stephan Schmidheiny, the former Swiss owner of the Eternit construction firm, and Jean-Louis Marie Ghislain de Cartier de Marchienne, a major Belgian shareholder, are being tried in absentia for contaminations from the 1970s.
Prosecutors have requested that the two -- Schmidheiny is now 64 years old and De Cartier is 89 -- should each be sentenced to 20 years in prison.
Some 6,000 people are seeking damages from the pair in an investigation that has lasted five years but is the product of a 30-year campaign by victims.
Judge Giuseppe Casalbore said the verdict would be delivered from February 13th.
The trial revolved around asbestos produced at four Italian facilities and includes employees who worked there as well as people living nearby.
The two defendants are accused of causing an environmental disaster and failing to comply with safety regulations, but their lawyers said they were optimistic.
"The trial did not demonstrate criminal responsibility for my client," said Guido Carlo Alleva, a lawyer for the Swiss billionaire.
Cesare Zaccone, who is defending De Cartier, said his client was not directly involved in the facilities, adding: "I am confident."
Asbestos, which was banned in Europe in 2005 but is still widely used in the developing world, had been used mainly as building insulation for its sound absorption and resistance to fire, heat and electrical damage.
Exposure to the fibrous mineral can cause lung inflammation and cancer.