The city of Charleston is doubling its reward —from $25,000 to $50,000 — for anyone whose tip leads to a big break in solving a string of peninsula arson cases.

Charleston Mayor Joe Riley announced the move today, saying the city’s arson task force recommended the increase.

The bigger sum is not related to a person who police want to interview in connection with an early Saturday morning fire at 54 Vanderhorst St. The city has released a sketch of a man in his early 20s who warned a resident about the first, helped douse it and then left.

The $50,000 sum includes $45,000 in city money and $5,000 from the S.C. Insurance News Service. It would be paid to someone whose information led to the arrest and conviction of a person — or people —who have set the fires.

At least 85 suspicious fires have broken out north and south of the Septima P. Clark Parkway since 2000, according to The Post and Courier’s analysis of police and fire reports. Most were set between midnight and 5 a.m. in porch areas and at homes rented by young people.

Riley and Police Chief Greg Mullen declined to say much about the status of the investigation another than to say it’s ongoing.

Anyone with information about any of these fires is asked to call 1-800-92ARSON, 1-800-922-7766.

Read more in Friday’s editions of The Post and Courier.