My educated guess is Erickson couldn't smell the taint on Bryan from that distance, but he already knew Marco was a Nocturnal. It's a pheremone thing, not visual with the ringers. 

Cardinal to Pope Siglericus l

That would make sense. And thanks for answering cause I hadn't even though of this question but when it came up I was trying desperately to grasp any kind of answer. 

"Urban legends go well with parmesan and horror. In fact their name is conveniently one and the same: Stevie."

Erickson already knew who gatinau was and what he looked like, that's why he was the target... and as far as he knew the other two were cops, who he wouldn't attack at all... unless he was faced with a ringer and his 'accomplices'.... 

SynapticJam on Toast - hhhmmm... tastes like chicken (aka PUVJK)

-so it would make sense that this sense is needed in telling if one is of the children/saviors or not (of the "human" babies of marie)
http://www.pgholyfield.com/maah/

-do yuo now something we don't?
http://www.pgholyfield.com/maah/