NEW YORK (CBSNewYork) — The family of a man who has been behind bars for nearly 20 years says he’s innocent and new evidence in the case will finally prove that.

“I will keep coming back again, and again, and again until he’s free,” Jon-Adrian Velazquez’s mother, Maria, said. “He’s innocent.”

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As CBS2’s Jessica Borg reported, she had some star power on her side – Martin Sheen in the past and actress and activist Alfre Woodard on Tuesday.

“I felt it was my obligation as a free woman and as a citizen,” Woodard said.

Velazquez’s lawyers announced Tuesday that three months ago, through a source, they received an old police report with information that proves his innocence. They claimed the report was withheld by the Manhattan district attorney’s office before the trial.

“It must be turned over. Our Constitution mandates that, because a prosecutor’s job is simply to seek justice, not just a conviction,” attorney Robert Gottlieb said.

The case began in 1998 in Harlem. A former police officer who ran a gambling den was gunned down in a robbery. Velazquez, then a 21-year-old father of two, was arrested after witnesses picked him out of a lineup.

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But his lawyers said there is key information in the police report. The father of one of Velazquez’s co-defendants described his son’s friend as a “black male, light complexion, with braided hair.” The same description was used in the original police sketch of the shooter.

“That description did not match the description of Jon-Adrian Velazquez,” Gottlieb said.

Velazquez’s lawyers have now filed a motion in New York Supreme Court to have his conviction overturned.

The Manhattan district attorney’s office responded, saying, “The suggestion that this office concealed any information is false.”

“The existence of the police report in question was disclosed to the defendant’s legal team in 1999, prior to the trial. This is the latest in a series of unsuccessful legal challenges brought by the defendant over the years,” the office said.

Four years ago, the district attorney’s office re-investigated the case with its Conviction Integrity Unit, but decided there was insufficient proof to overturn Velazquez’s conviction.

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Velazquez’s family hopes a new trial will clear his name – if a new trial is granted.