More than 13 years after the police shooting of Amadou Diallo, Commissioner Raymond W. Kelly has agreed to restore a service weapon to one of the four New York City officers involved, a decision that Mr. Diallo’s mother characterized as a betrayal.

Mr. Kelly had indicated “that he was not going to give back the gun,” Kadiatou Diallo said in a phone interview from her home in Maryland. “Now he has turned around and given back the gun. We want to know why. Why did he change his mind?”

The police fired 41 shots, killing Mr. Diallo as he stood in the vestibule of his apartment building in the Bronx on Feb. 4, 1999. Although the officers said they believed he had a gun, Mr. Diallo was unarmed.

The Police Department offered no official explanation on Tuesday about restoring a gun to the officer, Kenneth Boss. But a law enforcement official familiar with Mr. Kelly’s reasoning pointed to the recent exoneration of another officer, Michael Carey, who fired 3 of 50 bullets shot at Sean Bell, who was killed on the morning of his wedding outside a Queens nightclub in 2006.