The Vanishing Painting

One suspect is lying. Can you find them?

Tuesday, 20:40.
The night guard's torch lands on an empty frame. “Girl by the Lake” is gone from the second floor of the Harbor Museum.
The storm
Tuva: “Fact.”
A storm knocked out all power across the whole block, museum included, from 20:30 to 21:15. Not even the emergency lights came on.

Everything you need is in this file. The suspects are Pim, Borka, Fnuss and Knut. Tuva never lies on a case.