The CBI on Friday arrested former Indian Air Force (IAF) chief S.P. Tyagi on charges of corruption in its ongoing probe into the Rs 3,600-crore AgustaWestland helicopter deal.S.P. Tyagi was arrested from Delhi along with his cousin Sanjeev Tyagi alias Julie Tyagi and a Delhi-based lawyer, Gautam Khaitan. S.P. Tyagi, his cousins Sanjeev, Rajiv and Sandeep and 10 others, including some European middlemen, were named in an FIR which the Central Bureau of Investigation lodged in March 2013.