The screen of share prices is seen turning almost red at an Asia Commercial Bank (ACB)'s securities trading floor in Hanoi on August 22, 2012. Vietnam's largest stock market keeps plunging after Vietnam police arrested Nguyen Duc Kien, a top banking tycoon on suspicion of illegal business activities. The benchmark VN Index on the Ho Chi Minh City Stock Exchange fell 1.59 percent at 410.23 on August 22, extending yesterday's 4.7 percent plunge, the biggest drop since October 2008.