Having recognized it as magecraft, the bowman—Alkeides—let his attention wander around the area while continuing to deflect the police officer’s prosthetic hand with his bow.
He discovered a distortion in the scenery.
It was a crude illusion. No ordinary person would ever have seen through it, but it was obvious to a Heroic Spirit of Alkeides’ caliber.
“...So, you’ve come out of your hole, mage.”
Alkeides judged that it was Berserker’s Master and immediately grasped what the shadows meant.

Fate/Strange Fake: Volume 5, Chapter 15 ("Gold & Lions II")