Anna Duritskaya , 23 , pleaded to be allowed home to her native Ukraine but was said to be under police guard for further questioning . The girlfriend of murdered Russian politician Boris Nemtsov was under armed guard at an unknown location last night , as tens of thousands marched in Moscow in his name . The former deputy prime minister and leading critic of Vladimir Putin was gunned down as he walked home from dinner on Friday with Anna Duritskaya . The model , 23 , pleaded to be allowed home to her native Ukraine , but was said to be under police guard yesterday for further questioning . She is understood to have given a description of the killer , despite partial ‘ memory loss ’ from ‘ deep shock ’ , a law enforcement source said . As an ‘ immediate eyewitness ’ , there were ‘ grounds to conduct additional investigative action regarding her ’ , the source added . Last night it emerged the head of Russia ’ s Investigative Committee , Alexander Bastrykin , who will lead inquiries into the murder , is a Putin loyalist with a history of intimidating the Press . He once threatened to behead a journalist and investigate the killing himself . Ukraine ’ s consul in Moscow , Gennady Breskalenko , said Miss Duritskaya was questioned until 5am on Saturday at the Investigative Committee building , where he had tried to see her . Ostap Semerak , a Ukrainian MP , said the model ’ s parents were concerned . He said Miss Duritskaya told them by phone that she had ‘ no idea where she is kept ’ , only that she was ‘ taken to some flat which is guarded , and she is not allowed to leave ’ . Associates of Mr Nemtsov said she was staying with a friend . The opposition leader had organised the protest against Russia ’ s involvement in Ukraine , but it became a mourning rally , with chants of ‘ Russia without Putin ’ . Police claimed 16,000 marched , but observers said there were up to 70,000 , with several thousand more in St Petersburg . David Cameron said he was ‘ shocked and sickened by the callous murder ’ and that Mr Nemtsov was ‘ dedicated to speaking up tirelessly for the Russian people , demanding their right to democracy and liberty … and to an end to corruption ’ . Mr Nemtsov , 55 , a former nuclear scientist , rose to prominence under Boris Yeltsin , after the Cold War , becoming deputy prime minister in 1997 . Scroll down for video . The 23-year-old model and the opposition leader had dinner in central Moscow before Mr Nemtsov was gunned down on a bridge overlooking St Basil 's Cathedral . Miss Duritskaya is said to have suffered partial memory loss . Thousands of people took to the streets of Moscow to protest against his murder with any attributing blame to the Russian President . The 55-year-old was shot four times by an unknown killer . He was a vocal critic of Putin throughout his career . After leaving parliament in 2003 , he founded opposition movements and was a vocal critic of Mr Putin over Ukraine , the economic crisis and corruption . Voters in Estonia appear to have turned away from a party that supports closer ties with Moscow . Pollsters say first returns , based on online voting , heavily favour the Reform Party of Prime Minister Taavi Roivas , with 37.5 per cent , more than the 28.6 per cent it won in 2011 . The opposition Centre Party , which supports closer links with Moscow , had just 7.7 per cent – compared with the 23.3 per cent it won in 2011 . But it is thought these voters have less access to the internet . A married father of four , he is understood to have been with Miss Duritskaya for three years . She was unharmed when he was hit by four of seven bullets fired from a white Lada on a bridge near the Kremlin . Mr Nemtsov had warned that Mr Putin wanted him dead . But the Kremlin strongly denied any official responsibility for the killing . Investigators said they were looking at the possibility he was killed by opposition figures , or that Islamic extremists targeted the Jewish politician . In an interview hours before his murder , Mr Nemtsov accused a ‘ mad ’ , ‘ aggressive ’ Mr Putin of lying over the Ukrainian conflict and called his rule a ‘ catastrophe ’ . The president wrote to Mr Nemtsov ’ s mother , promising to ‘ do everything ’ to ensure the perpetrators are ‘ properly punished ’ . The government is offering £31,500 for information leading to the killer . Vladimir Putin has denied any involvement in Mr Nemtsov 's death . The government is offering £31,500 for information leading to the killer .
Anna Duritskaya , 23 , watched as Boris Nemtsov was shot four times . The Ukrainian model has been questioned extensively by Russian police . She has pleaded to return to Ukraine but is being held in a safe location . Thousands marched in Moscow in protest against Mr Nemtsov 's death . Critics claim the 55-year-old was killed for publicly condemning President .