A 23-year-old Ukrainian model who was with slain Russian opposition leader Boris Nemtsov when he was shot dead has said she did not see the gunman who pulled the trigger.
The emotional account by Anna Duritskaya in a TV interview came amid speculation about who was responsible for the high-profile assassination near the Kremlin in Moscow and what it means for Russia.
While state-run and Kremlin-controlled media focused on a theory that the killing was a provocation aimed at staining president Vladimir Putin, critics are holding the Russian leader responsible for creating an atmosphere that encouraged the crime by fanning nationalist, anti-western sentiments and vilifying the opposition.
Ms Duritskaya said she has been questioned extensively by authorities.
Shortly after midnight, she flew into an international airport in the Ukrainian capital, Kiev, from where she was swiftly whisked away by a security detail in a car with blacked-out windows.
Vadim Prokhorov, a lawyer for Mr Nemtsov who travelled with Ms Duritskaya, said she had been left emotionally drained by investigators' questioning.
"She has given a full and exhaustive account of her last hours with Boris," Mr Prokhorov said.
"If any further investigative action is required, she has promised - something she has done publicly - that she will cooperate.
"The main thing is that the guilty parties be tracked down."
In her first public comments since the killing, Ms Duritskaya said in an interview with Russia's independent Dozhd television that she waited for Mr Nemtsov to meet her on Friday night at the Bosco Cafe, a restaurant in the former GUM department store on Red Square.
He had just given a radio interview in which he had slammed Mr Putin's "mad, aggressive policy" on Ukraine.
They dined and then walked across a bridge near St Basil's Cathedral, heading for Mr Nemtsov's apartment across the Moscow River from the Kremlin, she said.
Ms Duritskaya said she did not see the man who shot Mr Nemtsov, only aware of a car speeding up.
"I don't know where he came from, but he was behind," she said of the gunman.
"I didn't see the man. I turned round and all I saw was a light-colored car. I saw neither the brand nor the licence plate of the car that was driving away."
After Mr Nemtsov was shot, she saw a snowplough approaching them on the bridge and she said she asked its driver how to call police.
The driver gave her the number, then drove away, she added.
TV Center, a station controlled by the Moscow city government, broadcast a poor-resolution video from a web camera that it said showed Mr Nemtsov and Ms Duritskaya shortly before he was killed.
A vehicle that TVC identified as a snowplough 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 video, which could not be independently verified, contradicted the initial statement by police, who said Mr Nemtsov was shot from a passing car.
Investigators said they are looking into several possible links for Nemtsov's slaying, including an attempt to destabilize the state, Islamic extremism, the Ukraine conflict and his personal life.
They have offered a reward of three million rubles (more than €43,000) for any information.
Tens of thousands of supporters marched on Sunday through central Moscow in a silent tribute to Mr Nemtsov. Others mourned him in St Petersburg and other European cities.
Mr Putin quickly sent condolences to Mr Nemtsov's 86-year old mother, promising her that the perpetrators of the "vile and cynical murder" will be brought to justice.
State television stations focused on allegations that Russia's enemies could be behind the hit, following comment by Mr Putin's spokesman that the president saw the attack as a "provocation" aimed to destabilise the country.
Chechnya's Moscow-backed strongman, Ramzan Kadyrov, openly blamed western special services for the shooting.
Kremlin critics pointed out that the site of the killing is one of the most heavily secured parts of the Russian capital, packed with police, plainclothes agents and security cameras.
"The choice of place in front of the Kremlin ... points at the perpetrator's sense of impunity and his link to law enforcement structures," opposition politician Ilya Ponomaryov wrote in his blog.
"It was made for a picture: a prominent Russian opposition leader lying dead with the Kremlin stars and St Basil's Cathedral as the backdrop."
Many commentators said that like other key opposition leaders, Mr Nemtsov was constantly shadowed by police, so it would be hard to imagine his killing could go unnoticed by them.
Some noted that Mr Nemtsov died on the newly established holiday commemorating the Special Operations Forces, honouring troops who swept through Ukraine's Crimean Peninsula, setting stage for its annexation by Russia a year ago.
Mr Nemtsov's killing was the biggest political assassination in Russia since another Kremlin foe, journalist Anna Politkovskaya, was shot dead in the lift of her Moscow apartment building on Mr Putin's birthday in 2006.
Five Chechens were convicted in the case last year, but it has remained unclear who ordered the killing.
Some observers speculated that certain members of a hawkish, isolationist wing of the government could have had a hand in Mr Nemtsov's death, possibly counting on it to provoke outrage abroad and further strain Russia's ties with the West.
Those relations already are at their lowest point since the Cold War because of the Ukrainian crisis.
Western officials have called for Russia to conduct a prompt, thorough, transparent and credible investigation into the slaying. Mr Putin has ordered law enforcement chiefs to personally oversee the probe.
White House spokesman Josh Earnest on Monday described Mr Nemtsov as a "tireless advocate for his country, an opponent of corruption, and an advocate for human rights and greater transparency."
The business newspaper Kommersant quoted anonymous sources in the Interior Ministry as saying there was no CCTV video 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 all cameras "belonging to the city" were operating properly when Mr Nemtsov was killed.
She said federal authorities also had surveillance cameras near the Kremlin that are not under her organisation's control.