RICHMOND, Va. (WJZ) — Lawyers for former Baltimore Police Officers Daniel Hersl and Marcus Taylor made oral arguments in their appeals before the 4th Circuit Court of Appeals in Richmond, Virginia, Friday.

The officers were part of a gun unit that prosecutors say violated citizens’ rights and committed overtime fraud, among other offenses.

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The panel of judges heard arguments about wiretaps and the way the charges were structured, but Hersl has gone beyond that in letters he wrote to a state commission.​

WJZ has obtained a series of 13 letters Hersl wrote — starting in April through last week — where he proclaims his innocence.​

In the letters to the Maryland Commission To Restore Trust In Policing, Hersl admits he had a reputation on the street as an “aggressive” officer but writes, “I am fully innocent, have nothing to hide and consider my input the morally and ethically right thing to do.” ​

He says he wants people to “understand the whole story” of what happened with the GTTF.​

It was before that same commission this week that Baltimore’s Police Commissioner admitted the Department had not started a promised internal review of the scandal.

“We have not done a deep dive to make the assessment of what happened with these individuals that were missed,” Commissioner Michael Harrison said Tuesday in Annapolis.​

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Hersl and fellow former Det. Marcus Taylor were the only indicted Gun Trace Task Force officers to fight the charges in court. Both got 18-year prison sentences for robbery, conspiracy and racketeering. Prosecutors say they stole money and drugs, submitted false reports, and committed overtime fraud.​

Hersl wrote, “The prosecutor capitalized on the overtime system being poorly administered, which he knew was totally mismanaged, and used the situation to twist my compensation/reward as being fraudulent.”​

He contends it was no secret to the police union and police brass that overtime was given in exchange for getting guns off the streets. Hersl wrote, “It was obvious the chain-of-command was fully aware of the squad’s work performance and encouraged its continuation by motivation through rewards.” ​

Hersl also claims he was a “good cop working with bad cops” and compares himself to Frank Serpico–a former New York City police detective who exposed widespread corruption in that department in the 1970s. ​

Hersl says he reported suspicions about two of his co-defendants–Momodu Gondo and Jemell Rayam–to his supervisor Sergeant Thomas Allers. He says Allers told him they were “not doing anything illegal and I had nothing to worry about.”​

Allers was also convicted and is currently serving a 15-year prison sentence. ​

Hersl is now serving his time at a federal prison in the Midwest. “My life was so entwined with the Baltimore City drug culture that one of the drug dealers I arrested on numerous occasions showed up in federal prison beside me,” he wrote. “While the majority of the police force took a laid back approach after Freddie Gray, the squads I as associated with took the risk, faced the danger and got the guns and drugs off the street.”​

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The trial judge has called the officers’ actions “an abuse of the public trust.” Hersl says he will continue writing letters to the commission.