Vietnam's stock market Tuesday suffered its biggest drop in nearly four years after police arrested one of the country's wealthiest banking tycoons, according to dpa. The VN-Index closed down 4.8 per cent at 416 points, the biggest one-day drop since November 10, 2008, after 257 of the bourse's around 300 stocks hit their maximum allowed drop of 5 per cent for the day. Nguyen Duc Kien was arrested on Monday evening for "alleged economic wrongdoings," Ministry of Public Security said, while the police said he was charged with "illegal business activities." "Many traders were very pessimistic, and panicked on hearing news Mr Kien was arrested," said Nguyen Khai, a trader at FPT Securities in Hanoi. "I think the market will drop further." "Pressure to sell remained strong among local traders, and will probably dampen prices of many blue-chips," she added. Kien, 48, faces charges in connection with three of companies he owns, including the Hanoi-Asia Finance Company, State Bank Governor Nguyen Van Binh told the National Assembly Tuesday. The authorities were not specific about the charges. The multi-millionaire, one of the country's 20 richest people according to stock reports, co-founded the Asia Commercial Joint Stock Bank, one of Vietnam's largest private banks, and is a major shareholder in several other commercial banks. He is also deputy chairman of the Vietnam Professional Football Joint Stock Co, which runs the V-League, and is chairman of Hanoi Football Club. Besides banking and football, Kien also put money into many other areas such as tourism and garments.