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JEFFERSON CITY, Mo. — A man sentenced to life in prison without parole on a marijuana-related charge walked out of a Missouri prison a free man on Tuesday, after spending two decades behind bars.

The release of Jeff Mizanskey followed years of lobbying from family, lawmakers and advocates for the legalization of marijuana, who argued that the sentence was too stiff.

This undated photo provided by the Jefferson City Correctional Center shows Jeff Mizanskey. Jefferson City Correctional Center via AP

Mizanskey was sentenced in 1996 after police said he conspired to sell 6 pounds of marijuana to a dealer connected to Mexican drug cartels. The life with no parole sentence was allowed under a Missouri law for persistent drug offenders; Mizanskey already had two drug convictions — one for possession and sale of marijuana in 1984 and another for possession in 1991.

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Mizanskey was the only Missouri inmate serving such a sentence for a nonviolent marijuana-related offense when Democratic Gov. Jay Nixon agreed in May to commute his sentence. Nixon's action allowed Mizanskey to argue for his freedom.

Nixon cited Mizanskey's nonviolent record, noting that none of his offenses involved selling drugs to children. The law under which he was originally sentenced has since been changed.

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Other states are reevaluating punishments for drug-possession crimes, largely motivated by the high cost of imprisoning low-level, nonviolent offenders.

In Connecticut, a new law will make possession of small amounts of hard drugs, including heroin, cocaine and crack cocaine, a misdemeanor for a first-time offense, rather than allowing for the current maximum seven-year prison sentence. Nebraska and Alabama expect to save hundreds of millions of dollars by cutting down on the number of offenders locked up for possessing small amounts of drugs under new laws.