Planting Potatoes In Chicago

So there's this old Pakistani man who lives alone in Chicago. One day he sends an e-mail to his son Ahmad :

"Dear son, I would love to plant some potatoes in the backyard but I'm old and lonely, I can't plow the land without your help. With love, your father."

Later that night, Ahmad responds :

"Dear dad, for the love of God PLEASE DO NOT TOUCH THE LAND ! I have buried "the thing" there. Your loving son, Ahmad."

That same night at 3 in the morning, 4 FBI agents broke into the father's house and investigated the backyard, inch by inch, without finding anything. They went away without being noticed.

Ahmad sent another email to his father : "Dear father, I am 100% positive that the land is now plowed. I couldn't have done it better myself. Ahmad."