The 23-year-old Ukrainian model who was with slain opposition leader Boris Nemtsov tearfully recounted Monday their last dinner in a chic Red Square restaurant and their walk onto a nearby bridge, but said she did not see the gunman who pulled the trigger. The emotional account by Anna Duritskaya came amid a swirl of speculation about who was responsible for the high-profile assassination 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, his 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.

Duritskaya said she has been questioned extensively by authorities. Shortly after midnight Tuesday, Duritskaya 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 Nemtsov who traveled with 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," 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, Duritskaya said in an interview with Russia's independent Dozhd television that she waited for Nemtsov to meet her Friday night at the Bosco Cafe, a pricey restaurant in the former GUM department store on Red Square. He had just given a radio interview in which he had slammed Putin's "mad, aggressive policy" on Ukraine. They dined and then walked across a bridge near St. Basil's Cathedral, heading for Nemtsov's apartment across the Moscow River from the Kremlin, she said, her eyes welling with tears. Duritskaya said didn't see the man who shot Nemtsov, only 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 license plate of the car that was driving away." After Nemtsov was shot, she saw a snowplow 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 Nemtsov and Duritskaya 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 video, which could not be independently verified, contradicted the initial statement by police, who said 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 3 million rubles (nearly $50,000) for any information.

Putin quickly sent condolences to 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 Putin's spokesman that the president saw the attack as a "provocation" aimed to destabilize the country. Chechnya's Moscow-backed strongman, Ramzan Kadyrov, openly blamed Western special services. 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.

Nemtsov's killing was the biggest political assassination in Russia since another Kremlin foe, journalist Anna Politkovskaya, was shot to death in the elevator of her Moscow apartment building on 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 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.