Allen Parmer is best known as the brother-in-law of Jesse and Frank James—with some accusations that he also rode the outlaw trail with them. But Parmer set his own path of violence during the Civil War.
He joined Confederate forces at the age of 13, in 1861, and later rode with Quantrill’s guerrillas. In that capacity, he gained a reputation as a killer—especially at the Lawrence, KS raid of August 23, 1863. Some veterans claimed the 15-year-old killed more men than anyone else.
https://truewestmagazine.com/gunfighters-didnt-always-shoot-straight/