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John Richard Knock realizes he’ll likely die in a 12-by-10-foot cell in federal prison.

Locked behind bars on a marijuana trafficking conviction, America's growing acceptance of the drug is cold comfort to the 66-year-old who was handed two life sentences, plus 20 years — for a first-time conviction.

“I don’t think about it, I just try and stay healthy,” Knock told FoxNews.com of his sentence via phone from the Allenwood Federal Correctional Complex in Pennsylvania. “I just wish society would look at this and say, ‘Hey is this fair?’”

The sentence makes Knock one of 3,278 prisoners recently identified by the American Civil Liberties Union who are serving life without parole for nonviolent drug and property crimes. Nearly four in every five were convicted of crimes involving drugs, including marijuana.

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While Knock, who prosecutors said was part of an international marijuana trafficking scheme, has been serving his time, the drug has become increasingly accepted. Recreational use of marijuana is now legal in Colorado and Washington, and 15 other states have also eased restrictions, most for medical purposes. In October, for the first time, a Gallup poll found that a majority of Americans now favor legalizing the drug after reaching 50 percent in 2011.

Knock said he’s aware of how seismic the shift has been regarding marijuana and public opinion surrounding the drug since he was locked up.

“They seem to be saying that what takes place in somebody’s home is their business, not the government’s business,” Knock said. “Society is changing … and people in government have made choices to try and correct society’s ills by attacking something they don’t understand. And they’re attacking it extremely hard.”

But Knock and most others serving life for pot convictions were typically traffickers and not simply users, some experts note. Profiting from drugs — even marijuana — is a far cry from puffing on a joint, they say.

"Those who traffic in illegal drugs, who prey on our nation’s youth with poisons that destroy bodies, minds, and futures, should find no refuge in the criminal justice system," John Walters, who was drug czar under President Bush, wrote in a 2007 report. "Long prison terms, in many cases, are the most appropriate response to these predators."

Knock’s sister, Beth Curtis, started lifeforpot.com two years ago to raise attention to her brother’s plight and other prisoners facing similar fates. She hopes that society's changing views on marijuana could prompt a review of the sentences of her brother and others.

“When public opinion reaches some kind of tipping point, I think most lawmakers will jump out in front of the issue,” she said. “I don’t see why they would find any value in continuing to oppose [legalizing marijuana] if their constituents want it legalized.”

Some attorneys contacted by FoxNews.com said Knock’s case is far from unique. Randall Brown Johnston, a Missouri-based criminal defense attorney who formerly worked as a prosecutor, recalled the case of Jeff Mizanskey, who was found guilty of possession of five pounds of marijuana in 1993 and was later sentenced to life without parole.

“This was a brutal sentence,” Johnston told FoxNews.com. “Unfortunately, the difference between one judge and another can make all the difference. This judge was particularly harsh and had a reputation for that.”

Prosecutors offered a plea deal of 25 years without parole to Mizanskey, but like many other prisoners who received particularly harsh sentences for nonviolent offenses, the defendant chose to go to trial, Johnston said.

He could have taken a plea and gotten off with a much lighter sentence, Pettis County prosecutor Jeff Mittelhauser told the Riverfront Times, which detailed his case earlier this month.

"He rolled the dice — and that's his prerogative, to go to trial — but he did, and this is what happened," Pettis County prosecutor Jeff Mittelhauser told the Riverfront Times.

But Johnston also hopes the changing opinion of pot can lead to relief for people doing life for marijuana-related crimes.

“There’s been a great change in public opinions about marijuana convictions,” he said. “It may take another 10 years for lawmakers to catch up and maybe go back and revisit the severity of the laws. But these laws are on the books right now and these are nonviolent people. It costs a huge amount of money to lock them up and people can go out and commit a murder or rape somebody and be sentenced to less.”

In the meantime, Mizanskey, the only inmate in Missouri serving life without parole for a nonviolent drug offense, has applied to Gov. Jay Nixon for clemency. But that is a long shot, according to Tamara Holder, a Fox News contributor and criminal defense attorney who focuses on clemency cases. She said pardons are rarely granted by governors unless they are soon leaving office.

“Our society is punitive in that not only have we created laws that don’t make sense, but we punish governors or look upon them as weak or playing a political card ... when they grant clemency,” said Holder, who has filed roughly 100 petitions for clemency.

Like Johnston, Holder believes a sea change could be coming.

“The fact that we’re seeing a more liberal, for lack of a better word, understanding of drug use in America, particularly marijuana, hopefully the tide is changing from the bottom up,” she said. “Hopefully it will slowly grow to changing some of these punitive laws.”

Knock, meanwhile, takes some comfort from what happens outside of prison, even if it leaves him little hope of being free. His son, Aaron, 22, recently graduated from Columbia University in New York with an engineering degree.

“I left him when he was 3 and I didn’t think I’d be gone for such a long time,” he said. “But I still have hope that society will come to realize what they’re doing.”