(NewsNation) — Lamar Johnson walked out of a St. Louis courthouse earlier this week as a free man for the first time in nearly three decades.

Johnson was only 21 years old when he was found guilty of murdering 25-year-old Marcus Boyd, who was shot on his front porch in 1994 by two people. Johnson always maintained his innocence, saying he was with his girlfriend miles away when the killing took place.

After multiple failed appeals and habeas corpus petitions, St. Louis Circuit Attorney Kim Gardner set out to help Johnson, citing misconduct by the investigation’s lead detective in 1995. She filed a motion in August seeking Johnson’s release, and the preceding work culminated in a judge’s decision Tuesday to vacate Johnson’s conviction.

“I am extremely grateful,” Johnson said Thursday on “CUOMO.” “In spite of the mistakes, there is still something to be happy and joyous about in the end of it, and that’s why I’m able to be grateful.”

While Johnson was convicted and sentenced to life, a second suspect, Phil Campbell, pleaded guilty to a reduced charge in exchange for a seven-year prison term.

Johnson testified at a December hearing that he was with his girlfriend on the night of the crime, except for a few minutes when he stepped outside of the home of a friend to sell drugs on a corner several blocks from where the victim was killed.

Johnson’s girlfriend at the time, Erika Barrow, testified that she was with Johnson that entire night, except for about a five-minute span when he left to make the drug sale. She said the distance between the friend’s home and Boyd’s home would have made it impossible for Johnson to get there and back in five minutes.

The case for Johnson’s release was centered around a key witness who recanted his testimony and a prison inmate who says it was he — not Johnson — that joined Campbell in the killing.

James Howard, 46, is serving a life sentence for murder and several other crimes that happened three years after Boyd was killed. He testified at the hearing that he and Campbell decided to rob Boyd, who owed one of their friends money from the sale of drugs. He also said Johnson wasn’t there.

James Gregory Elking testified in December that he was on the front porch with Boyd, trying to buy crack cocaine, when the two gunmen wearing black ski masks came around the house and began the attack. Elking, who later spent several years in prison for bank robbery, initially told police he couldn’t identify the gunmen.

He agreed to view a lineup anyway. Elking testified that when he was unable to name anyone from the lineup as a shooter, Detective Joseph Nickerson told him, “I know you know who it is,” and urged him to “help get these guys off the street.”

Saying he felt “bullied” and “pressured,” Elking named Johnson as one of the shooters. Gardner’s office said Elking was also paid at least $4,000 after agreeing to testify.

In March 2021, the Missouri Supreme Court denied Johnson’s request for a new trial after then-Attorney General Eric Schmitt’s office argued successfully that Gardner lacked the authority to seek one so many years after the case was adjudicated.

The case inspired a state law that give prosecutors a legal avenue to appeal cases in which they believe a defendant has been wrongfully convicted.

“As a prosecutor I take an oath, and I believe the oath is to pursue justice,” Gardner said of her motivation for helping Johnson. “Unfortunately, we have some individuals who believe finality is following the rule of law, but I don’t believe in that, and I believe that Missouri finally, on February 14th, 2023, had the will to correct Lamar Johnson’s wrongful conviction.”

Now a free man, Johnson is setting out to do everything he feasibly can. He hopes to find a job and enjoy experiences he was denied while behind bars.

“I want to see everything. Unfortunately I’ve never been outside of St. Louis, and so I’ve talked about how I would like to see the ocean, I would like to fly on a plane, ride a train, just about everything,” Johnson said. “Actually, I’ve been told I want to do too much.”

His daughter is preparing to get married, and it means “everything” to him that he will be able to share that memory with her.

“Every father looks forward to that day when he can be there to support her decision to move on with her life with somebody new,” Johnson said.

Despite being released, Johnson isn’t entitled to any compensation from the state. Gardner has her sights on that as her next mission.

“I have basically tasked the state legislature to change the law because in these cases like Lamar Johnson, there should be a mechanism for compensation,” Gardner said. “They pushed for the mechanisms to give me the ability to correct the wrongful conviction, now it’s do we have the will to totally compensate individuals like Lamar Johnson who have actual innocence, which is very different.”

Even though he lost 28 years of his life, Johnson says he doesn’t hold any ill will for the courts, the criminal justice system or the people who put him behind bars.

“I believe that holding onto hatred is just swapping one prison for another, and I’ve been in prison way too long to continue to carry that around with me,” Johnson said. “I understand that people make mistakes, you know, regardless of what causes that, and so I think there’s redemption for everyone.”

The Associated Press contributed to this report.