Shares of Gitanjali Gems plunged by another 5 per cent in morning trade as CBI tightened the noose on PNB offenders by arresting the vice president of Gitanjali Group of Companies. The agency yesterday arrested Vipul Chitalia in the Rs 12,636-crore PNB scam and claimed that he was a "mastermind" who reported directly to diamond trader Mehul Choksi. Reacting to the development, Gitanjali Gems stock slumped 5 per cent to hit its fresh 52-week low of Rs 17.45 on BSE. This is the 15th straight session of fall for the stock. It has lost as as much as 80 per cent since February 14, the day PNB fraud came to light. On NSE, the stock fell to a 52-week low of Rs 17.40. CBI says Chitalia had left the country in the last week of January, as did the prime accused Nirav Modi and Choksi. The fraud was allegedly perpetrated by Modi and his uncle Choksi, the promoter of Gitanjali Gems. It is alleged that they got LoUs and FLCs of Rs 12,636 crore issued in favour of foreign branches of Indian banks based on fraudulent claims.