Authorities are tracking the woman believed to have started four fires in northwest and southwest Fresno over the last five weeks.
In each incident, the suspect has posted handwritten notes on the residences and then used gasoline to ignite the fires.
Fresno Fire investigators are now asking the public to see if any additional letters have been posted or if anyone has any information on the suspect.
Fresno Fire is also looking for another arsonist who has been setting grass fires throughout the city.