According to the police, 42-year-old Harpal Singh Sodhi was arrested from Bhiwari in Rajasthan after which the child was rescued from Rewari Railway Station.
Sodhi's accomplice Harpreet, who is the father of a classmate of the rescued boy, is on the run and efforts are being made to nab him, police said.
Harpreet was allegedly the mastermind behind the kidnapping.
The boy, a resident of Rajinder Nagar here, had gone to a nearby market last evening to recharge his father's mobile phone but did not return home.
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A case of kidnapping for ransom was lodged at Rajinder Nagar police station.
"During the course of investigation, it was learnt that Harpreet had contacted the victim's parents last week for the purpose of purchasing a shop," Deputy Commissioner of Police (Central Delhi) Alok Kumar said
When Harpreet's family members were questioned, they told the police that he had gone out of Delhi for arranging money to buy the shop, he said.
Police said Harpreet is also a property dealer and he used to work with his friend Sodhi. He, however, managed to escape from the railway station during the rescue operation.
Several police teams were dispatched to various parts of Delhi and also to areas outside the city. The location of the person who made the ransom calls was established near Bhiwadi in Rajasthan through technical surveillance, they said, adding that a car which was used in the crime has been recovered.