Investigators believe a series of fires that broke out at four Hyannis homes over the weekend were the result of arson, a fire official said Monday. Firefighters responded to a report of a fire at 45 Pilgrim Lane around 4:20 a.m. Saturday, Barnstable police Sergeant Andrew McKenna said. Upon arrival, firefighters noticed smoke coming from nearby 33 Pilgrim Lane, and later discovered fires at 27 Pilgrim Lane and 135 Baxter Road, he said. The close proximity of the fires breaking out in such a short span of time suggests arson, said Jennifer Mieth, a spokeswoman for State Fire Marshal Stephen D. Coan. No one was injured in the blazes.