#14 Old Mr. Tidy

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 little visit. I noticed his study light was on so 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 the officer know Mr. Fiend was lying?