Firefighters are conducting an arson investigation after a string of suspicious fires in central Fresno on Wednesday morning. The first fire was spotted by a passing Fresno police officer at the St. Paul United Methodist Church on Clinton Avenue and Thesta Street around 1:00 am. The officer saw flames in the doorway. Investigators believe someone set the wooden doorframe on fire. Officials say the officer used a fire extinguisher to put out the blaze. Fresno firefighters used fans to move the smoke out of the building. Fire crews made sure there were no flames left smoldering. A couple of hours later, crews responded to a small fire at an apartment complex on Harvard and Mariposa Avenues in central Fresno. Investigators found a door jamb to a storage unit on fire. Fire crews were able to put out the blaze quickly.