welcome back to cnn newsroom. jihadi john grew up as a typical british kid. authorities say the child this this picture, mohammed emwazi went from pop groups and football to being a western front man in extremist videos. brian todd looks at the theories behind his radicalization. >> reporter: he's known around the world as isis' best-known killer a cold-blooded brit, who waves his knife terrorizes western leaders. and then shows an innocent hostage decapitated. he may have beheaded hostages on camera himself but gee had di john the man believed to be 26-year-old mohammed emwazi was a preppy british school boy from a middle-class family. he graduated from a large, well-regarded classroom in london with a computer programming degree. how and why did a young man with his prospects join isis? an advocacy group said it