Delhi Police Commissioner BS Bassi on Thursday joined the probe into murder of his mother Sunanda Pushkar.br br Shiv Menon today appeared before the Special Investigation Team at its office and was questioned in connection with the murder case.br br Menon reached the Vasant Vihar police station, also the office of the SIT, at around 1.15 pm.br br Bassi later said Menon has joined the investigation, which is under progress. He added that Menon is likely to throw light on many aspects in the case.br br Menon was not questioned earlier as he was out of India.