62-year-old Raju has been put on a ventilator and doctors attending on him were closely monitoring his vital parametres, family sources said.
They said the next 48 hours were crucial.
The soft-spoken Raju was appointed on January 19, 2009 as the first Chief of NIA set up in the wake of 26/11 Mumbai terror strikes.
A 1975 batch IPS officer of Jammu and Kashmir cadre, Raju handled the case of the US citizen Lashker-e-Taiba David Headley and led a team in breaking his estranged Moroccon wife Fauzia Outullah.
Before being appointed as NIA Chief, Raju was the Director General (Vigilance) of Jammu and Kashmir.
Considered as one of the finest officers, Raju was associated with probes into Rajiv Gandhi assassination case, hijacking of Indian Airlines plane to Kandahar in 1999 and Naval war room leak.
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Serving as head of the Vigilance Bureau in Jammu and Kashmir earlier, Raju streamlined the department which was in a shambles due to militancy.
His investigation had brought to light the alleged misappropriation by Maulvi Ifthikar Hussain Ansari, a former minister in Mufti Mohd Sayeed's cabinet.