Minutes into New Year’s Day 1987, a French couple visiting New York fell behind their companions while walking in Midtown Manhattan’s holiday crowds and were attacked.

The couple, Jean and Renée Casse, were on 52nd Street when Mr. Casse was robbed, assaulted and thrown to the ground. Days after Mr. Casse, 71, died from injuries to his neck and head, two people — Eric Smokes and David Warren — were arrested in the attack. By the summer, the two had been convicted.

For nearly the next four decades, Mr. Smokes, who was 19 when he was arrested, and Mr. Warren, who was 16, would try to clear their names without success. On Wednesday, under a new district attorney, the two men’s convictions were overturned and their indictments were dismissed.

“Eric Smokes and David Warren lost decades of their life to an unjust conviction,” said Alvin L. Bragg, the Manhattan district attorney, in a statement. “I am inspired by the unyielding advocacy of Mr. Smokes and Mr. Warren and hope that today’s decision can finally bring them a measure of comfort and justice.”

In months of hearings that started in November 2018, the Manhattan district attorney’s office fought an attempt by the men, who had been paroled years before, to have their convictions overturned.

A judge denied the defense’s motion in January 2020. Now, four years later, the office has reversed its position.