A security firm that sells AI weapons scanners to schools is facing fresh questions about its technology after a student was attacked with a knife that the $3.7m system failed to detect.

On Halloween last year, student Ehni Ler Htoo was walking in the corridor of his school in Utica, New York, when another student walked up behind him and stabbed him with a knife.

Speaking exclusively to the BBC, the victim’s lawyer said the 18-year-old suffered multiple stab wounds to his head, neck, face, shoulder, back and hand.