The incident happened last night and the mob allegedly dumped his body in an open field at Vijay Chowk area near Swaroop Nagar, police said.
Shankar lost consciousness due to the thrashing and he was dumped in the field.
The incident came to light at 7.15 am today after a passerby discovered the body and called the police control room.
The victim was sent to a nearby hospital where doctors declared him dead.
Shankar lived with his family at C-block in Jahangirpuri and was unmarried and jobless.
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It has also been found that the attackers attempted to change Shankar's clothes after his death, police said.
If these allegations are found to be true, the accused might also be charged with destruction of evidence along with murder charges.
The involvement of five persons was established when during the probe they met a local security guard, Jai Kumar, and learnt that he had witnessed the mob lynching.
"The attackers had pinned down Shankar and were thrashing him. Around a dozen men were standing and watching the thrashing as spectators. The guard was scared seeing the thrashing and neither informed police nor made an attempt to rescue the man," said a senior police officer
Police is probing whether Shankar was a thief. They are yet to establish the exact sequence of events that led to his murder.
Few persons have been detained in connection with the murder and the fact that he was lynched by the mob has been confirmed, said the officer.
Police is verifying his antecedents to find out if he was previously involved in any crime.