The Congress on Friday demanded a time-bound inquiry by a sitting Supreme Court Judge into the encounter killing of gangster Vikas Dubey near Kanpur earlier in the day "to expose those who gave protection to the criminal".

"To expose the people behind Vikas Dubey will be the only justice to eight martyred policemen. It is a litmus test for Union Home Minister Amit Shah and Chief Minister Yogi Adityanath," Congress Chief Spokesperson Randeep Surjewala told a press conference and raised a number of questions over the alleged encounter.

Surjewala claimed that the state was witnessing an unholy nexus between police and criminals. "When Dubey had surrendered (in Ujjain on Thursday), why would he try to run away? Who stopped the media vehicles just a few km from the spot of the encounter?" the Congress leader questioned.

The party alleged that Dubey was "just a pawn in the organised crime syndicate in Uttar Pradesh and the Chief Minister should tell the public who the head of this syndicate was.

The Congress leader further asked how the criminal reached Ujjain in Madhya Pradesh without any hindrance, and what all secrets he knew which could reveal the nexus of criminals and politicians.

"Why was Dubey's name was missing from the list of top 25 criminals in UP?"

The Congress leader said that even though a chartered plane was sent to Madhya Pradesh, he was brought back by road by police and how could he end up in a TUV when he was last seen seated in a Tata Safari SUV.

Surjewala further asked how could the gangster be hit in the chest if he was trying to flee. "Also, there were no skid marks on the road at the spot where the vehicle overturned. All these circumstances raise questions," he added.