So by now it is an open secret that he killed Nobuo, pretty much everyone knows about it, but how?
Is it because Tetsuo went and stupidly published a novel detailing his murders on the internet for the world to see? na that can't be, is too obvious.
But then how did this guy find out while the Syndicate is still going the roundabout way? maybe he was stalking Reika for a while, or maybe she told him about how Nobuo was abusing her and that then one day he suddenly left after her dad found out, and thus is assuming that Tetsuo killed him?