Loki knew the hand of those drawings straight away. He could admire the soul in the portraits and feel that it came from darkness and a pit of emptiness inside him rather than an admiration. The work was tortured beauty, not empty happiness full of shallow demeanour.
He wanted it. He wanted to look into Rogers's soul and find his way in but the book was secured in the maniac's hands. He would need to be smarter than that, especially with the phone in his hands.