Seth Harris, a lawyer for 43-year-old Jose Vargas, says the jury handed down the verdict Tuesday in state Supreme Court in Brooklyn.
The city's law department says it plans to file an appeal.
Harris says police arrested Vargas in September 2006 on a drug-related charge. During the arrest, Harris says officers took Vargas' bag containing his insulin.
He says Vargas complained he needed the insulin as he was taken to a precinct and then to central booking, where he suffered a seizure in a jail cell.
Harris says Vargas now lives in a nursing home and is confined to a wheelchair.