A veteran black lawmaker urged prosecutors to reopen investigations of 10 bombings that rocked homes and churches during the yearlong Montgomery bus boycott, which was begun in 1955 after Rosa Parks refused to give up her seat on a bus to a white man. With 50th anniversary events starting this week, the legislator, State Representative Alvin Holmes, a Democrat, sent memorandums to federal, state and local prosecutors requesting investigations into the bombing of five homes, four churches and a cab stand during the boycott. Mr. Holmes said "99 percent of the bombings were never investigated." A spokeswoman for the United States attorney in Montgomery said Mr. Holmes's memorandum had been forwarded to the appropriate investigative agency.