A man locked up for 18 years after being wrongfully convicted in a double-murder case is poised to get $3.5 million from San Francisco.

City Attorney Dennis Herrera has recommended the city settle the lawsuit by Caramad Conley for that amount, documents newly introduced at the Board of Supervisors show. The settlement still must be approved by the board, which is to take up the matter this month, but supervisors routinely approve such settlements. Police Chief Greg Suhr and the city’s Police Commission have already signed off on it, the documents show.

Conley, 40, was locked up in 1992. In 1994, he was convicted and sentenced to serve two life-without-parole terms for a 1989 double slaying on Third Street that prosecutors said was gang-motivated. A judge ruled in December 2010 that he had been wrongly convicted. He was released a month later.

San Francisco Superior Court Judge Marla Miller found that police investigators knew that the prosecution’s star witness, Clifford Polk, lied on the stand about whether he was being paid, but they did nothing to intervene. Miller concluded that the lead investigator in the case, Earl Sanders — who later became police chief — knew about the perjury “and did not correct it.”

One of Conley’s lawyers in the criminal case, Daniel Purcell, said earlier that Sanders started paying Polk — an unemployed transient with a history of drug dealing — three months before Conley’s trial. Purcell said Polk was getting weekly payments, and he said Sanders acknowledged in a 2010 deposition that he made those payments. The payments totaled thousands of dollars, and police also provided Polk with the use of a house.

It is the second case where the city is preparing to pay a multimillion dollar settlement after a judge tossed out a murder conviction involving Sanders and his partner at the time, Napoleon Hendrix.

In 2009 the city agreed to pay $7.5 million to Antoine Goff and John Tennison, who were both freed in 2003 after spending more than 10 years in prison.

In that case, the courts found that prosecutors and police had information that another person might have committed the crime but did not disclose it during the trial.

Conley sued the city and Sanders in January 2012 in U.S. District Court, alleging civil rights violations.