A 4-year-old boy was thrown to his death from the roof of his seven-story apartment building in Brooklyn by his 20-year-old brother on Saturday, the police said.

The brother, identified by the police as Shawn J. Smith, was charged with second-degree murder. The police said he had no criminal record and there was no history of involvement by the Administration of Children’s Services at the home of the boy, Shimron Smith.

Around 3:30 a.m., Mr. Smith approached two uniformed officers responding to a 911 call in the 70th Precinct, a few blocks from Shimron’s apartment in the East Midwood neighborhood, which is in the 63rd Precinct.

“I need to talk to you,” he said, according to the police. The officers finished with their call and then continued their conversation with Mr. Smith, who told them: “My brother may be hurt. He might be dead.”