Dreaded gangster Prem Prakash Singh alias Munna Bajrangi was shot dead allegedly by another inmate inside the district jail in Baghpat on Monday, the police said.
Terming the incident as serious, Chief Minister Yogi Adityanath has ordered a probe.
Four jail officials have been suspended in connection with the incident.
Bajrangi was brought here from Jhansi Jail on Sunday and was to be produced in a local court on Monday in a case of demanding extortion money from BJP MLA Lokesh Dixit.
Bajrangi, who was also named in the killing of former BJP legislator Krishnanand Rai, was shot dead allegedly by another inmate, police said.
At a press conference recently, the gangster's wife had alleged that conspiracies were being hatched to kill her husband.
Principal Secretary, Home, Arvind Kumar said Jailor, Udai Pratap Singh, Deputy Jailor Shivaji Yadav, Head warden Arjinder Singh and warden Madhav Kumar have been suspended in connection with the incident.
A probe by a judicial magistrate will be undertaken as per procedure, he said and added an FIR has been lodged in the matter.