It's stated that Ethan he dialysis four times a day, some people believe this to be a mistake as haemodialysis (where the blood is pumped through a machine) is done once a day. However, peritoneal dialysis, which is what Ethan seems to be on, is a type of home dialysis which is performed up to 5 times a day.
The assassin left his thumbprint on the table when he moved it to the window. His fingers were covered by the realtor's handkerchief but not his thumb. FBI would have found it.