The Ukrainian woman with Kremlin critic Boris Nemtsov when he was gunned down told Russia media on Monday that she did not see his killer, as conflicting reports emerged about the availability of surveillance footage showing the slaying.

No suspects have been arrested since Nemtsov was shot dead Friday night. According to Russian investigators, he was walking home on a Moscow bridge near the Kremlin with a woman when he was shot four times by an assailant, who then escaped in a light-coloured car.

The area is one of the most secure, heavily monitored parts of the Russian capital. The attack came just hours after a radio interview in which the opposition leader had denounced Russian President Vladimir Putin's "mad, aggressive policy" in Ukraine.

Investigators say they are looking into several possible motives for Nemtsov's slaying and have offered 3 million rubles (nearly $50,000 US) for information. Many of Nemtsov's supporters hold the Kremlin responsible, saying it created an atmosphere that encouraged the crime by vilifying the opposition and fanning nationalist, anti-Western sentiments.

Witness under police guard

The Ukrainian woman that Nemtsov was with when he was shot — 23-year-old Anna Duritskaya — has been under police guard for questioning since early Saturday. But in an interview Monday with the independent Russian TV channel Dozhd, she said she had not seen Nemtsov's attacker.

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Anna Duritskaya poses for a photo for a modelling portfolio in Kyiv. Duritskaya was the sole witness of the killing of Boris Nemtsov. (Daria Buznikova/Associated Press)

"I didn't see anything," she told Dozhd. "I turned around and all I saw was a light-coloured car. I saw neither the brand nor the licence plate of the car when it was driving away."

Duritskaya, who said she had known Nemtsov for three years, said she had been questioned exhaustively by police and wants to leave the country but Russian investigators will not let her do that. She is now staying at a friend's apartment in Moscow.

She also told Dozhd that, after the shooting, she asked a nearby snowplow driver how to call the police. The driver gave her the number then drove away, she said.

Mother worried

Duritskaya's mother Inna, who spoke to The Associated Press in Kyiv, the Ukrainian capital, said she had been in touch with her daughter. She said Anna was very upset and she worried that Russian authorities were "putting psychological pressure on her."

"I am worried that they want to use her, as a citizen of Ukraine, use her as though this situation is somehow something to do with Ukraine," she said Monday. "She has absolutely nothing to do with this killing. She was not politically active. She had nothing to do with Boris's political activities."

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Russian Foreign Minister Sergey Lavrov said the investigation into the killing of opposition leader Boris Nemtsov must not be interfered with. (Pavel Golovkin)

The business newspaper Kommersant, meanwhile, quoted anonymous sources in the Interior Ministry as saying there was no CCTV footage of the killing because the cameras in question were not working at the time.

However, Yelena Novikova, a spokeswoman for Moscow's information technology department, which oversees the city's surveillance cameras, said Monday that all cameras "belonging to the city" were operating correctly on the night of Nemtsov's death. She said federal authorities also had surveillance cameras near the Kremlin that are not under her organization's control.

Novikova would not confirm the existence of any video of the killing, saying the police investigation was still underway.

Poor-resolution video

Meanwhile, TV Center, a station controlled by the Moscow city government, broadcast a poor-resolution video from one of its web cameras that it said showed Nemtsov and his date shortly before he was killed. A vehicle that TVC identified as a snowplow moved slowly behind the couple, obscuring the view of the shooting. TV Center then circled what it said was the suspected killer jumping into a passing car.

The authenticity of the TVC video could not be independently confirmed.

In Geneva on Monday, Russian Foreign Minister Sergey Lavrov called the Nemtsov killing a "heinous crime which will be fully investigated." He told the UN Human Rights Council that Putin had "immediately handed down all instructions and is ensuring special control over this investigation."

At the same time he rebuffed outside interference in the probe, saying any "attempt to use the heinous killing of Boris Nemtsov for political purposes is despicable."

Tens of thousands of supporters turned out Sunday to march through central Moscow in a silent tribute to Nemtsov, while other supporters mourned him in St. Petersburg and other European cities.

Prominent Russian opposition leader Alexei Navalny has asked to be released early from prison so he could attend Nemtsov's funeral, which is being held Tuesday at a human rights center in Moscow.

France's foreign minister called Nemtsov's killing an "assassination that was revolting" and called Monday for a serious investigation into it.

"The fact is that it is not good to be an opposition figure in Russia," the minister, Laurent Fabius, told BFM television.