The criminal has been identified as Kamal, cops said.
One of the undertrials, who escaped from police custody after miscreants opened fire at a jail van in Sambhal district, was killed in an encounter Saturday night, the police said.
Kamal, who, along with Shakeel and Dharampal, was freed by unidentified assailants after carrying an audacious attack at the van, was killed in an encounter with police at Gawan-Sambhal road under Adampur police station, a police spokesman said.
A search operation, under Superintendent of Police, Amroha, Vipin Tada and other top officials, is going on to search the other wanted criminals, he said.
A police constable was also injured in the gunfight, the spokesman said, adding he has been hospitalised.
On Wednesday, two policemen were killed in Sambhal when the unidentified assailants opened fire at the jail van and helped the three undertrials escape from the custody.
The incident took place at Dhannumal crossing near Banither village in the district when a police van returning with 24 undertrials prisoners to Moradabad after hearings in a Chandausi court was attacked by some persons, Additional DG (Law and Order) PV Ramashastri had said.
The two policemen were identified as constables Harendra and Brijpal.
Following the incident, the Uttar Pradesh police had said its Special Task Force (STF) was tasked with nabbing the unidentified assailants.