The Palwal police on Friday again questioned Mukesh Lakhanpal, the husband of the Delhi woman who was found murdered on NH-2 on September 28.
"Apart from Mukesh, 15 others have been questioned in the past few days," said Jagat Singh Hooda, superintendent of police, Palwal. He said the 15 included staff of the Agra hotel where the couple had stayed, attendants of the toll plaza, a liquor vendor and a business partner of Mukesh.
Satvinder Lakhanpal was found murdered in the bushes off the highway while Mukesh was found lying near her body with his legs and hands tied.
They were travelling from Agra to Delhi. They lived in Mayur Vihar.
The cops had earlier questioned Mukesh on Monday as well as some of his relatives in Delhi.
Police said when the couple stopped their car near toll plaza close to Aurangabad in Palwal to answer the call of nature, four car-borne armed youth reportedly came from behind and kidnapped them.
The assailants tied them both and looted cash, gold jewellery before killing Satvinder.