The bridge has been standing since 1889 and is listed on the National Register of Historic Places.
The fire was started using an accelerant on the stairs.
This investigation remains ongoing.
"It was determined that Henderson was responsible for the fire."
Sheriff's arson detectives responded to the scene about 1 a.m. Tuesday.
The property belongs to Bradley Bisbee and the heirs of Leland R. Bisbee.
"She does need to see and meet with one or two psychiatrists. She’s being treated in jail right now with mental health concerns."
A body was found inside the 2.5-story wood frame structure and was sent to medical examiners for identification.
"We still do not know what caused the explosion. The investigation is far from over, we still have a lot ahead of us."
"A great job was done by the firefighters tonight in limiting the effects of the fire on both the museum and its displays."