A traveling clothing salesman was sentenced on Friday to 75 years to life in prison for killing three merchants in Brooklyn in a series of attacks that had shopkeepers on alert for months, prosecutors said.

The man, Salvatore Perrone, 67, of Staten Island, was convicted last month in State Supreme Court in Brooklyn of three counts of second-degree murder. Justice Alan D. Marrus sentenced Mr. Perrone to the maximum penalty allowed.

In three attacks in 2012, the authorities said, Mr. Perrone went into stores in Brooklyn around closing time, when the merchants, who were all of Middle Eastern origin, were alone. He opened fire with the same sawed-off rifle in each attack. When he was arrested, he had been planning to attack again, the police said.