Although Shard and Mr. Barton's party didn't leave the house through the same door, the heavy bloodstains on Professor Magis made him very noticeable when Shard circled to the back alley of the house.
Especially in foggy weather, those halos were like highlighted bars in the field of vision:
"Circle Sorcerers of the Truth Society, they couldn't have just killed someone, could they?"
In order to avoid being spotted while tracking, Shard didn't call for a carriage but walked through the city with Mia Cat.
He walked fast and left the downtown area about an hour later, entering the suburbs south of the city. However, the bloodstains did not head into the mountains but turned into the estate area at the foot of Sicarl Mountain where local nobles resided.
A month earlier, the Spiritual Practice Order had opened the Interstice passage in the nearby "Russell Estate".