The arrested have been identified as Nandini, Arvind and Rajesh, B S Jaiswal, Deputy Commissioner of Police (Outer), said. Two others, Hardwari and Vicky, are yet to be arrested.
The three were allegedly involved in the murder of 70-year-old Gurmeet Kaur, who retired from the IT Department.
Kaur was found murdered in her Rohini residence on September 12 with her hands and legs tied to a rope and her mouth taped and her maid Nandini was missing.
Suspicion fell on Nandini as it came to light during investigation that she had introduced herself as Sonia or Sonu at some other places where she was working.
Kaur had also told his daughter Inderpal Grover that Nandini and her husband were coming to her house to take the sofa after getting a telephone call from the maid.
Kaur has been living alone for the past few years as her husband died 22 years ago and her daughters lived elsewhere. Her son is living abroad.
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"Nandini offered Kaur to purchase the old unused sofa at a very good price. Kaur agreed and then Nandini requested her that her husband wished to see the sofa. She brought her associate Hardwari along with her and introduced him as her husband.
"Hardwari on the pretext of seeing the sofa, observed the house from the point of view of feasibility of committing dacoity," Jaiswal said.
Later, all the five came to the house on September 12 and allegedly murdered her before ransacking the house.