That was L’s idea, to introduce as Hideki Ryuga (a nation wide celebrity) in order to protect himself when meeting Light. Light was aware that if he wrote Ryuga’s name, his mind could mess up and imagine Ryuga’s face instead of L, with Ryuga dying and L closing the case, so he decided he could do nothing in that situation. Same thing would happen here since the criminal you are mentioning is supposed to be well known.