There are figures that suggest a different picture, but hardly anyone knows them. In 2013, the former Schwyz public prosecutor Lorenz Müller wrote a “behavioral analysis of serial arsonists”. Based on a survey of German-speaking Swiss cantons, he examined 19 series of fires with a total of 21 perpetrators. Of these 21, three were current and one were former firefighters - their share was therefore just under 20 percent. Müller’s conclusion: the firefighter as arsonist is not “such an unjustified cliché” after all.

translated paragraph from https://www.nzz.ch/gesellschaft/loeschen-was-der-kollege-angezuendet-hat-ld.1815687

There were many arsonists who were actually firefighters:

https://en.m.wikipedia.org/wiki/Firefighter_arson

Those indeed came back to the scene.