(Portland, OR)  --  Police are seeking the public's help in their search for a person who stabbed a transient man to death at a Portland bus stop nearly eight years ago.  Police say 50-year-old Donald Ray "Pokey" Polk was killed eight years ago yesterday at a bus shelter on Southwest 1st and Sheridan Street.  Crime Stoppers of Oregon is offering a reward of up to 25-hundred dollars for information that leads to an arrest.