The accused was identified as Jitender alias Jitu, a resident of Najafgarh.
The doctor, who owns a hospital in Dwarka Mor, approached the police on December 12 complaining that several WhatsApp calls were being made by some men but he could not attend the calls, a senior police officer said.
A day earlier, five men arrived at the hospital in a car and two of them barged into the premises with pistols. When they did not find the doctor, they asked the staffers there to tell the doctor that he will have to face dire consequences if he fails to pay Rs 1 crore as demanded, the officer said.
Following the complaint, police started looking for the accused. Many suspected hideouts in and around Delhi were raided but they escaped narrowly, the officer said, adding that however, on Tuesday, Jitender was zeroed and later arrested by a joint team of police.
Both the gang leaders are in jail and they need money to fighting cases and to keep affiliation of gang members intact, police said.
One mobile phone was recovered from Jitender's possession, the officer said, adding that efforts are on to nab the other accused.
(With inputs from agencies.)