Where did you find that he substituted on the 19th? First I've heard that.
http://www.timesdaily.com/apps/pbcs.dll/article?AID=/20060818/NEWS/608180335/1011
" ... Seven days before 6-year-old JonBenet Ramsey died, the man who told authorities he "accidentally" killed her was finishing the semester at Vina School as a substitute teacher.
Records from the Franklin County Board of Education indicate John Mark Karr worked as a substitute teacher from Dec. 17 to Dec. 19, 1996. Ramsey was found dead in the basement of her Boulder, Colo., home Dec. 26, 1996, authorities said.
Former Vina Principal Johnny Hester said that after the 1996 Christmas break, Karr continued to serve as a substitute teacher at Vina in early 1997 and throughout that year. ..."