That was all it took for a thief to take the bag, which held his computer, calender, keys and other documents. The professor said he was most saddened by the loss of his calender: "It is my life. I have documented everything in it that has happened in the last 10 years and beyond."
The professor then called the police to report the incident and cancelled his credit cards. Much to his surprise, however, he returned to the stairwell a couple of hours later and found the backpack returned, with everything in it except for his notebook and a library card.
One week later, the story gets even more interesting as the professor returned home from class to find an envelope waiting in his mailbox that had a USB flash drive in it. The drive was full of all of the professor's data from the notebook.
"I am very happy," says the professor. "This story makes me feel hope for humanity."