Plea may aid probe into '92 slaying Victim worked at Logan k By Patricia Nealon GLOBE STAFF A former Northwest Airlines baggage handler charged with lying to a federal ' grand jury investigating the 1992 murder of fellow baggage handler Susan Taraskiewicz pleaded guilty yesterday to blocking the investigation. Robert Brooks admitted to one count of obstruction of justice before US District Judge Richard G. Stearns. The guilty plea, which could bring Brooks a sentence of 15 months to more than eight years in federal prison, raises the possibility that he may now cooperate with federal investigators probing a link between Taraskiewicz's murder and a stolen-credit card ring that involved Brooks and a key suspect in Taraskiewicz's murder. But since there is no plea agreement in the public record that would indicate whether Brooks has agreed to help investigators, the clearest indication of whether he is cooperating will come when he is sentenced Jan. PLEA, Page B3