Seven former Boston police officers, all African-Americans who were fired after testing positive for cocaine in drug tests using samples of their hair, sued the police department yesterday, alleging the screening technique is biased against African-Americans. Rheba Rutkowski, an attorney at Bingham McCutchen who represents the former officers, said scientific literature indicates that the texture of African-American hair as well as the hair products they use could skew the results of a hair test. She also said hair tests are easier to pass if an employee has light hair, and that stray molecules can bind to African-American hair, altering the results. [continues 976 words]