Six persons, including three "prime witnesses" in the Sunanda Pushkar death case, were put through a lie detector test, Delhi Police Commissioner BS Bassi said amid indication that a number of other witnesses may be asked to undergo the examination.

"Our investigation is continuing and whatever is required to be done will be done. So far we have carried out polygraph tests on six persons. If there is any requirement we will conduct further tests," Bassi said.

Last month, the Delhi police had approached a city court for permission to carry out polygraph test on Narain Singh, who is domestic help of Sunanda Pushkar's husband and Congress MP Shashi Tharoor, driver Bajrangi and family friend Sanjay Dewan.