There was an article on Lou Marsh and his death in the old Saturday Evening Post (the weekly one). I sang the song for years, and once had the article. No longer, alas. Didn't take too much digging to find the citation though.
Death Of A Youth Worker Samuels, Gertrude // Saturday Evening Post;4/6/1963, Vol. 236 Issue 13, p74 Profiles Lou Marsh, former leader of the street gang called Young Untouchables in New York. Description of his personality and family life; Names of people who killed Marsh; Views on his death.