The murder of Boris Nemtsov, a political foe of Russian President Vladimir Putin who was publicly critical of the government, was reportedly caught on tape.

Nemtsov, 55, a first deputy prime minister under President Boris Yeltsin in the 1990s, was killed near the Kremlin late Friday, a day before his planned protest against the Russian government, as he walked from a restaurant after having dinner with his girlfriend, Ukrainian model Anna Duritskaya.

On Friday evening, Nemtsov and Duritskaya left the restaurant and began walking to Nemtsov’s apartment. They reportedly walked across a bridge, where a white car drove up. Then, Nemtsov was shot four times.

“If we can stop the campaign of hate that's being directed at the opposition, then we have a chance to change Russia."

- opposition politician Gennady Gudkov

According to the BBC, footage airing on Russian television showed a white Lada Priora car in the area; still, there is no clear signal the vehicle was involved in Nemtsov’s murder. One part of the film shows someone running in the road alongside the Great Moskvoretsky Bridge and jumping into the waiting car, which then sped off.

The exact whereabouts of Duritskaya are unknown since the killing, according to the Ukrainian Embassy.

According to UAToday, Ukrainian MP Ostap Semerak said that Russian law enforcement officials have forcibly detained Duritskaya in a private apartment and are not allowing her to be assisted by the Ukrainian Consulate.  She has, however, occasionally been in contact, the news agency reported, although it is unclear with whom.

The news of the video came as tens of thousands marched Sunday on Staraya Square in Moscow, turning the planned opposition march -- which was to be led by Nemtsov – into a mourning rally led by Nemtsov’s allies and supporters.

Following his role as a deputy prime minister, Nemtsov later became a prominent opponent to Putin, helping organize street protests and exposing official corruption.

“If we can stop the campaign of hate that's being directed at the opposition, then we have a chance to change Russia. If not, then we face the prospect of mass civil conflict,” opposition politician Gennady Gudkov told Reuters ahead of Sunday’s rally.

Dmitry Peskov, a Putin spokesman, said the Russian president had noted "that this cruel murder has all the makings of a contract hit and is extremely provocative," the BBC reported.

Pro-Kremlin activists reportedly said they would not disrupt the march.

The Associated Press contributed to this report.