Flash Crash of 2010, they find the man responsible

The man responsible for the 2010 "flash crash" has been found and now being tried for charges such as wire fraud, commodities fraud, commodities manipulation and spoofing. He would buy stocks and then quickly sell them giving false hope that the money he would be investing would benefit the company. He would make close to $800 a day. He found a way to beat the system and make alot of money doing it, but also costing others a lot of money in the process, that is why he is in trouble. Why is the stock market susceptible to an event such as this. how can one man do this to an entire economy.