(CNN) [Editor's note: A prior version of this story called Alejandro García Padilla the governor of Puerto Rico. He is a former governor.]

President Barack Obama's commutation of the sentence of Oscar López Rivera, who was convicted for his role in a Puerto Rican nationalist group linked to bombings in US cities, ends a decades-long fight to free a man who supporters call a "political prisoner."

Law enforcement officials have labeled him a terrorist since the 1970s.

López Rivera, who was serving more than 50 years in prison for plotting to overthrow the US government, belonged to Armed Forces of National Liberation, known by its Spanish acronym FALN. The group often fought for Puerto Rican independence through violence and was connel

In 1981, López Rivera was sentenced to 55 years in prison for "seditious conspiracy" and other felonies. He was later sentenced to an additional 15 years in 1988 for conspiracy to escape; to transport explosives with intent to kill and injure people; and to destroy government buildings and property.

López Rivera wasn't charged directly in FALN's attacks but more broadly with charges of plotting to overthrow the US government.

His prison sentence was expected to expire in 2051, but he will walk free on May 17, 2017.

Lopez Rivera was sentenced to 55 years in prison in 1981.

Multiple groups, including the Congressional Hispanic Caucus, the Congressional Black Caucus and other elected officials lobbied the Obama administration for López Rivera's release.

Melissa Mark-Viverito, the New York City Council speaker who was among the politicians who advocated for López Rivera's release, told CNN affiliate NY1 that the day was historic.

Mark-Viverito said López Rivera's imprisonment for an "unjust number of years" was based solely on his political beliefs.

"He is a political prisoner," she added.

Obama's commutation reduces the sentence being served, but it does not change a conviction, whereas a pardon forgives a certain criminal offense.

The FALN had claimed responsibility for bombings in the 1970s.

Joseph Connor, whose father Frank was one of four people killed in the January 1975 bombing of the historic Fraunces Tavern in Manhattan, called the commutation a "travesty" and "disgraceful."

Joseph Connor was 9 at the time of the lunch-hour attack -- for which FALN claimed responsibility. López Rivera was not convicted in connection with the bombing.

"He's never shown any remorse for what he did," Connor said. "We went to his parole hearing in 2011 and had he shown any contrition at all, had expressed any atonement, any sympathy, we would have been willing to forgive him and would have recommended that he be released. But he has shown none at all. He has no atonement and no contrition."

History of attacks

FALN first announced itself in 1974 , when it took credit for five bombings in New York.

The group was responsible for dozens of bombings and incendiary attacks during the decade, according to law enforcement officials. The bombings were called terror attacks and resulted in at least five deaths and more than $3 million in property damage, according to a 1999 House report for the Committee on Government Reform.

In one attack for which the group claimed responsibility, a booby-trapped body was used to lure a NYPD officer into an abandoned building. The resultant explosion permanently disabled the officer.

The statement taking credit for the attack warned: "(To) make it clear, for every repressive action taken against our communities or against FALN. independentistas, we will respond with revolutionary violence.''

In late 1976, Chicago police uncovered a bomb factory run by FALN, a discovery that led to the arrest of López Rivera, the House report said.

In 1999, then-President Bill Clinton offered clemency to 16 FALN prisoners who had been incarcerated while fighting for an independent Puerto Rico through violent means. Fourteen accepted the offer, but López Rivera was one of two prisoners who declined.

"None of them were convicted of doing bodily harm to anyone. And they had all served sentences that were considerably longer than they would serve under the sentencing guidelines which control federal sentencing now," Clinton said at the time.

"I did not believe they should be held in incarceration -- in effect -- by guilt by association," he said.

Clinton said he received petitions on behalf of the prisoners from hundreds of people, including former President Jimmy Carter, South African Archbishop Desmond Tutu, other religious leaders and congressmen.

The decision sparked strong criticism from law enforcement officials and some political leaders.

Supporters celebrate

López Rivera's supporters include "Hamilton" writer and actor Lin-Manuel Miranda, who said he was "sobbing with gratitude" about the news.

"Sobbing with gratitude here in London. Oscar Lopez Rivera is coming home. Thank you, @POTUS."

Sobbing with gratitude here in London.

OSCAR LOPEZ RIVERA IS COMING HOME.

THANK YOU, @POTUS.

🇵🇷 https://t.co/IEdaEvsVcG — Lin-Manuel Miranda (@Lin_Manuel) January 17, 2017

Miranda followed up the tweet with one addressed to Mark-Viverito, the New York City lawmaker.

"(And) @MMViverito, when you talk to Don Oscar, (tell him) I've got a show for him in Chicago. It'll be my honor to play Hamilton the night he goes."

Y @MMViverito, when you talk to Don Oscar, díle I've got a show for him in Chicago. It'll be my honor to play Hamilton the night he goes.

🇵🇷 — Lin-Manuel Miranda (@Lin_Manuel) January 17, 2017

Miranda hasn't played the title role in his Pulitzer- and Tony-winning production since July 2016.

Mark-Viverito, the first Puerto Rican and Latina to hold a citywide elected position in New York, replied: "Claro @Lin_Manuel! (Without) a doubt! Told him you would invite him to Hamilton. But no idea you would perform! What a treat! But he deserves it!"

Rep. Nydia Velazquez, D-New York, told CNN affiliate NY 1: "Being characterized as a terrorist himself, the White House took its time to assess every level, every fact, but most importantly this is a President who is very cautious, who is very respectful of the law."

"Today is a day of celebration. It's a day of brotherhood and sisterhood in PR and we are very proud and I'm very grateful to the president."

Puerto Rico's former governor, Alejandro García Padilla, also celebrated the decision on Twitter.

El pueblo de PR acaba de recibir las mejores noticias y comienza a celebrar la tan esperada decisión de @POTUS. pic.twitter.com/bt4wOHFL1z — Alejandro (@agarciapadilla) January 17, 2017

"The people of PR have just received the best news and are starting to celebrate the long awaited decision of @POTUS," he tweeted.

He called López Rivera's incarceration "a fight for all Puerto Rico."

Enhorabuena por la liberación de Oscar López. Esto fue una lucha de todo Puerto Rico. Gracias @POTUS. - AGP — Alejandro (@agarciapadilla) January 17, 2017

"Congratulations on the release of Oscar López. This was a fight of all Puerto Rico. Thanks @POTUS. - AGP" he added.

Mass pardons

On Tuesday, Obama granted commutation of sentence to 209 prisoners and pardons to 64 more, including the commutation of sentence to former Army soldier Chelsea Manning , who was convicted of stealing and disseminating 750,000 pages of documents and videos to WikiLeaks.

The President also pardoned James Cartwright, the former vice chairman of the US Joint Chiefs of Staff, who pleaded guilty in October to a single charge of making false statements to federal investigators in 2012 when he was questioned about leaking top secret information on US efforts to cripple Iran's nuclear program to two journalists.