PROVINCETOWN, Mass. -- A suspected arson fire has been solved in Provincetown. The sun did it.

The Cape Cod Times reported one of 20 fires under investigation was solved when Charles Welsh figured out that a long burn mark on his outdoor shower wall came from the sun reflecting off his shaving mirror.

"I'm a little chagrined at my stupidity," Welsh told the Times.

On Friday, an arson investigator from the state Fire Marshal's Office confirmed the fire was suspicious.

The Cape Cod town has had 20 fires deemed suspicious in the past six months, and the fire at Welsh’s house appeared to be the first where an arsonist targeted an occupied building.

But Welsh said he got a few calls from people who said the burn marked looked like the work of the sun, after they saw the picture of his outdoor shower printed in the Cape Cod Times.

“You can cross No. 20 off the list. Apollo did it,” Welsh told the Times.

Police are actively investigating the 19 other fires. The state fire marshal urged people to be vigilant in helping solve the crimes.