In 1997, Walter Johnson stood before Judge Frederic Block in a Brooklyn federal courtroom after being convicted of robbery, cocaine possession and witness tampering, just the latest in a troubling series of crimes that involved guns, drugs and violence.

Judge Block called Mr. Johnson, a street legend known as King Tut, “a classic example of a person who has to be incapacitated so society is protected against you.” Then he hit Mr. Johnson with five life sentences.

On Thursday, Judge Block called the punishment he imposed 27 years ago too harsh, the product of ill-considered laws and his own inexperience. He freed Mr. Johnson, who hours later walked out of prison and back into society.

“Judges gain insights that with the passage of time only can come with experience on the bench and their judicial maturation,” Judge Block wrote in his decision granting Mr. Johnson’s petition for release. He added: “Just like prisoners who have evolved into better human beings during their lengthy periods of incarceration, judges also evolve with the passage of years on the bench.”

At 90, Judge Block is a senior jurist on the same federal bench in the Eastern District of New York from which he sentenced Mr. Johnson as a second-year judge. He has seen shifts in sentencing standards and wrestled with the issue enough to prompt him to publish a book last month that presents some of his past cases in making the argument for revisiting overly punitive sentences.