The Delhi Police interrogated Rohit Shekhar Tiwari's wife Apoorva at her residence for the third consecutive day on Monday, sources said.
Rohit Shekhar was allegedly smothered to death on April 16.
The sources said that experts from the Forensic Science Lab, Rohini also visited Rohit Shekhar's home in Defence Colony on Sunday where they recreated the crime sequence and opined that no signs were found which showed that he had resisted while he was smothered.
The team also conducted an examination of the vehicle in which Rohit Shekhar was made to lie down before being shifted to the ambulance.
On Monday, Apoorva, along with her two domestic aides, was taken by police for questioning. She was also questioned on Sunday and Saturday.
Police are collecting evidence to strengthen their case and sources said they are close to cracking it.
Police sources said there are seven CCTV cameras at Rohit Shekhar's home, but two of them do not work.
"Rohit had gone to Uttarakhand to vote on April 12 and returned on the night of April 15. He could be seen on CCTV taking the support of the wall while walking in an inebriated state. No one has come and gone out of the home at the time Rohit was smothered," they said.
His mother Ujjwala on Sunday had alleged that her daughter-in-law Apoorva and her family were money minded people and wanted to acquire the entire property. She claimed that she would make more revelations in the near future.
Rajiv is my relative and has served to our family since long. He was also OSD to late N D Tiwari, she said.
She denied reports of Rohit Shekhar having affair with anyone.
"Apoorva's family wanted to take control of the properties of my both sons, Siddharth and Rohit, because this house is near to the Supreme Court where Apoorva is practising law," Ujjwala said, adding Apoorva was disappointed and expressed her displeasure over the fact that Rohit Shekhar's brother Siddharth wanted to give Rajiv's son, Karthik, a share in the property