Old Mr. Tilly was found dead in his study by Mr. Foster. Mr. Foster recounted his dismal discovery to the police. "I was walking by Mr. Tilly`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. Foster for the murder of Mr. Tilly. How did he know Mr. Foster was lying?
Frost forms on the inside of the window, not the outside. So Mr. Foster could not have wiped it off to discover Mr. Tilly`s body.