After the incident with the shadow man, knights around the city were looking around every little corner to see if they could find anyone suspicious but they had come up with nothing. This meant that the shadow man was most likely long gone by now.
Once the search party was called off, Wilfred had come back to Ray's room and interviewed each of the students individually to see if there was anything he could find out from them. After speaking to each of the students they all said the same thing. They could see a man wrapped around in shadows but nothing else.
This confirmed Wilfred's fear. Wilfred perhaps thought that he might have been seeing things when he saw the man but the students confirmed his thoughts, it was a true infected human. Unlike the Dark Guild members who drank the purple liquid, a true infected had been possessed first hand by the Shadow plague.