the Fatwa Department Research Committee - chaired by Sheikh `Abd al-Wahhâb al-Turayrî
May Allah reward you for carrying out the duty of enjoining what is right and forbidding what is wrong.
He knows that interest is unlawful. He simply does not care. If your concern is his talking openly about his misconduct to the students, then you may like to tell him that if these students follow him in his evil ways because of his influence, then they he shares in their sins without their sins being diminished in the least.
The Prophet (peace be upon him) also said: “All of my nation receives pardon except those who openly broadcast their sins.”
Source: Islam Today