Munna Bajrangi was part of Gajraj Singh's gang in Jaunpur and later joined Mukhtar Ansari's gang.
The pistol used in the murder of gangster Prem Prakash Singh, alias Munna Bajrangi has been recovered, the police said.
Additional Director General (Law and Order) Anand Kumar said, "As many as 10 used cartridges, 2 magazines and 22 live cartridges have also been recovered."
"The pistol used in the murder was recovered from a drain," he told PTI.
Mafia Munna Bajrangi was allegedly shot dead by another gangster inside Baghpat jail in Uttar Pradesh, hours before he was to be produced in a local court in a case of extortion from a former BSP legislator, the police said.
Uttar Pradesh Chief Minister Yogi Adityanath termed as "serious" the killing of 51-year-old Bajrangi, who was listed as an accused in 40 criminal cases, including those of murder and extortion, and ordered a probe.
Ten empty shells of a .762 bore weapon and some live cartridges were recovered from inside the district jail, Deputy Inspector General (Law and Order) Praveen Kumar told reporters.
"Three probes - one by jail authorities, another a magisterial inquiry besides a judicial inquiry - are going on in the matter," he said, adding that an FIR in the matter was lodged by jail authorities.
Munna Bajrangi was transferred with full security from Jhansi to Baghpat jail yesterday and was to be produced in a local court today in a case of demand of money from former BSP MLA Lokesh Dixit in 2017, Mr Kumar said.
Munna Bajrangi was allegedly killed by Sunil Rathi, who is also a gangster and had been in Baghpat Jail since July 31 last year, the officials said. Sunil Rathi was taken into custody and interrogated.