A、The raid had been photographed by hidden cameras. B、The raid had been witnessed by someone else. C、The bank teller proved that

Joe Smith had been brought up in an orphanage. He envied people who were rich and decided that when he grew up he could make a lot of money.
    Unfortunately, Joe was not clever and he failed all his school exams. "[26]I will either have to find a good job or I will have to become a thief. " Joe said to himself. He knew he would never find a well-paid job.
    For several months Joe watched a bank out of town. He noticed when it had the fewest customers. He watched, waited and planned.
    One afternoon he found that only two tellers were on duty. "I will either succeed and be very rich or fail and go to prison, " said Joe. He was willing to take the risk.
    Then he walked in and pushed a demand note over the counter. The teller read it, turned pale and quietly opened a small safe behind him. He took out $ 50, 000 and placed the bank notes in Joe’s open bag. Then Joe ran as fast as he could. That night, he chose a deserted piece of land near the house to bury money in case the police caught him.
    The next day he was woken by bangs on his door. He answered and there came two policemen. "Joseph Smith, you are under arrest for robbing a bank! "
    Joe protested in vain.[28]The bank had hidden cameras and the whole raid had been photographed. Joe was caught and sent into prison.
    Ten years later Joe was set free. He made sure no one was following him and quickly made his way to the spot where he had buried the money.
    Neither happiness nor money waited for him, however. A big building had been built on the site.
26.What did Joe think he had to do to become rich?
27.How did Joe successfully get money from the teller?
28.Why was the police be able to prove that Joe had robbed the bank?