A longtime sales supervisor for the Massachusetts State Lottery was fired Tuesday after he was seen cashing winning instant tickets, a state official said, sparking fear that the lottery’s supposedly strict security protocols may have been violated.

David Cannistraro, a $100,000-a-year employee who had worked for the lottery since 2002, was first placed on paid administrative leave in June after another lottery employee saw him cashing tickets at a store on Cape Cod, said Chandra Allard, chief of staff at the state treasury.

Lottery officials believe he was not just playing the lottery — which is prohibited by state law for lottery employees and their immediate families — but may also have been helping himself to tickets that were returned to the New Bedford district office but were still active and could be cashed.