Puzzle-10

Old Mr. Tidy was found dead in his study by Mr. Fiend.

Mr. Fiend recounted his dismal discovery to the police.

"I was walking by Mr. Tidy's house when I thought I would just pop in for a visit. I noticed his study light was on and I decided to peek in from the outside to see if he was in there. There was frost on the window, so I had to wipe it away to see inside.

That is when I saw his body. So I kicked in the front door to confirm my suspicions of foul play. I called the police immediately afterward."

The officer immediately arrested Mr. Fiend for the murder of Mr. Tidy.

How did he know Mr. Fiend was lying..?

ANSWER :

Frost forms on the inside of the window, not the outside.

So Mr. Fiend could not have wiped it off to discover Mr. Tidy's body.