The accused were identified as Sweta Panchal, Kuldeep Kaur, Pradeep and Manoj Solanki. It was Panchal who headed the gang, said a senior police official.
According to police, it was Kaur who allegedly targeted the doctor and developed good contacts with him.
On the evening of October 19, she sent a woman patient to the doctor's residence at Pitampura for medical consultancy. The patient, identified as Rukhsar, requested the doctor to escort her to a nearby bus stand as she felt a little unsafe there.
The duo then took the doctor to the office of their associate Solanki, a property dealer at northwest Delhi's Karala, and started negotiating.
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They allegedly demanded Rs 50 lakh, but later the matter was settled at Rs 30 lakh.
They also made the doctor to sign a note asking the woman to forgive him and threatened him that they could now use the note as evidence in the case.
He later approached the police and a case of hatching criminal conspiracy and charges was registered at Hari Nagar police station, said Kumar.
On Wednesday, the police asked the doctor to contact the accused on the pretext of handing them over the balance amount and laid a trap. Kaur and Solanki were arrested immediately. During interrogation, they spilled the beans and led police to Panchal and Pradeep.