New Delhi, Jul 13 (PTI) A key witness of the 1984 anti-Sikh riots, whose testimony was recorded by CBI last year in New York, today died at AIIMS following a massive heart attack. "Gyani Surinder Singh died following a heart attack at AIIMS," senior advocate H S Phoolka, who has been appearing for the riots' victims, said. Surinder Singh, who alongwith other key witness Jasbir Singh, had recorded his statement before CBI investigators in USA last year in the case in which Congress leaders Jagdish Tytler was under the scanner. The CBI, however, gave the clean chit to the Congress leader. The witness, who later came to India, was being harassed by the police at the instance of Tytler, Phoolka alleged. "His passport was taken at the IGI airport, minutes after the flight landed here," the advocate claimed.