The inmate, who was serving life sentence, attacked Aayush Pugalia inside the toilet in the jail this morning, DIG prisons Yogesh Desai said.
Preliminary investigation suggested that the incident was the fallout of an enmity between them, police said.
An investigation was on, police said, adding that further details were awaited.
Pugaliya was lodged in the Nagpur Central jail since 2011 in connection with the killing of eight-year-old Kush Kataria here in October 2011.
Kataria, the son of a local businessman, was abducted from his residence in Nagpur for a ransom of Rs 2 crore and then killed by Puglia.
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