After recovering, Pottu Amman was put in charge of the Tiger Organization Security Intelligence Service (TOSIS), the LTTE's intelligence wing, in mid 1988. Following the IPKF withdrawal in March 1990 and under Pottu Amman's leadership, TOSIS expanded greatly and became a formidable organisation, copying the tactics of Inter-Services Intelligence, Mossad and Shin Bet. As chief of TOSIS, Pottu Amman is believed to have masterminded the assassinations of Rajiv Gandhi, Ranasinghe Premadasa, Ranjan Wijeratne, Clancy Fernando and many others. He also played a key role in the unmasking of the "conspiracy" against LTTE leader V. Prabhakaran by deputy leader Mahattaya. Pottu Amman is believed to have tortured Mahattaya and extracted his "confession". In 1993 two separate divisions were created in TOSIS - National Intelligence Division and Military Intelligence Service. Pottu Amman was in charge of the National Intelligence Division as well as being in overall charge of TOSIS. He was later in charge of the LTTE's Chiruththaigal (leopard) commando division. In 1997 he was appointed military commander of Jaffna peninsula.