Being charged with a crime you didn't commit is a nightmare. Spending months behind bars when police knew all along you absolutely could not have done it is an outrage.

Both things happened to Raheem Crews of Roosevelt. He spent four months in jail because a now-retired Nassau County detective who knew Crews had an airtight alibi kept that key information to himself. Crews was the victim of a poisonous mix of carelessness and malice that should shake the faith of anyone who unquestioningly trusts police to treat everyone fairly.

He was arrested May 27, 2005, charged with a March 26 knifepoint robbery in Roosevelt and jailed until Sept. 29, 2005. But three days after his arrest, a second suspect in the robbery told then-Det. Nicholas Lemma that Crews, then 19, was in jail when the crime occurred. Lemma checked jail records on June 1, 2005, and confirmed Crews was incarcerated March 24 to 31.

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"I kept it to myself and said let the chips fall where they may," Lemma said in a 2009 deposition. He testified later that it just slipped his mind. Nassau taxpayers deserve better from their highly paid police, and now they will have to pay for those lapses.

The Crews case was a fiasco from the start. Police got the date of the robbery wrong in paperwork processed the day he was arrested. It indicated April 26 rather than March 26. Police blamed a typographical error.

A different detective who talked to witnesses about Crews' whereabouts on the day of the robbery discovered some confusion about the date. He left a phone message July 13 alerting the assistant district attorney on the case. But the paperwork error wasn't confirmed and corrected until Aug. 15.

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With the correct March 26 date established, Crews' family told his attorney he had been in the Nassau County jail when the robbery happened. The district attorney's office didn't learn that until late September. Lemma testified in a grand jury but never mentioned the ironclad alibi he'd known about for months. So Crews was indicted Sept. 8.

It was Sept. 27 before a judge was officially told of the alibi. Finally, on Sept. 29, 2005, after 125 long days in jail for a crime the lead detective on the case knew Crews did not commit, Crews was freed. Unsurprisingly, in May 2006, he sued Lemma, Nassau Police and others for false arrest.

In a perverse way, Crews was lucky he'd spent the night of the robbery in jail. But even that was the result of a law enforcement error, according to his attorney, Frederick Brewington. Crews was on probation in Nassau for misdemeanor criminal mischief, but he moved to Queens. His case was to be transferred, but when he contacted officials in Queens, they had no record. They told him to wait for a call from Nassau. A month passed. No call. So Crews, trying to do the right thing, contacted probation officials in Nassau who said a warrant had been issued for his arrest for violating probation. That's how he landed in jail.

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Last week, a federal jury in Central Islip found Lemma liable for malicious prosecution, but rejected a claim against the county for failing to properly train and supervise the detective. Lemma retired in 2009 with his full pension. Crews was awarded $175,000.

That's a paltry sum for stolen freedom.