What is one reason why the main character in Tell Tale Hearts is NOT insane?

Here's my opinion. He took the time to conceal his crime. Therefore, he knew that it was wrong to kill the man. Since he knew that his act was wrong,he knew the difference between right and wrong and therefore must have been sane. It would be 1st degree murder because it was premeditated. He spent seven nights creeping onto the room before he actually committed the murder, so it was not done on the spur of the moment. This is just my opinion, but I think it's worth considering.