be known as jihadi john. the isis executioner, unmasked while this morning his network of london extremists is uncovered. britain's prime minister vowed to pursue the jihadists. >> when there are people anywhere in the world who commit appalling and heinous crimes against british citizens we will do everything we can with the police with the security services with all that we have at our disposal to find these people and put them out of action. >> reporter: mohammed emwazi was a computer student at london's university of westminster. at the time it's alleged extremist groups met on campus. >> we've also seen evidence of jihadist videos being shared with the islamic society of the university, including those calling for the deaths of coalition soldiers overseas. >> reporter: and this is emwazi as a grade-schooler in 1998 who wrote on his yearbook that he liked "the simpsons."