What do you mean by three seconds in a row?
It won't be a serial killer in three seconds. Three-second combo comes from the game Crossing the Fire Line, which requires players to kill 6 people within 18 seconds, which means that the combo can be full, which means it is not a three-second combo. Crossing the line of fire is a first-person shooter game developed by SmileGate in Korea and operated by Tencent Computer System Co., Ltd. in Shenzhen.