Postal Inspectors evidence

The video tutorial discusses the story of a person who took precautions to cover his tracks but was eventually caught with marked bills and other stolen items. He confessed promptly, similar to many others before him, both amateurs and professionals. The tutorial highlights the lesson learned by Decker, who discovered that tampering with the mail leads to trouble.

How does the text describe the individuals involved in similar situations?

What did Decker learn about tampering?