Moscow theater hostage crisis

Thousands of people are expected to gather in Moscow on Sunday afternoon to honour the memory of assassinated Russian opposition politician Boris Nemtsov.

UN Secretary General Ban Ki-moon has condemned the assassination of Russian opposition politician Boris Nemtsov and said he expected the perpetrators "to be brought to justice swiftly."

Nemtsov was gunned down on 27 February in central Moscow by unknown assailants. Russian authorities have announced an investigation into the case.

Russian President Vladimir Putin has told murdered Boris Nemtsov's mother that "everything will be done" have the perpetrators and organizers "punished."

In a telegram to Ms Dina Yakovleva Eidmann published on the Kremlin's website, Putin has called the event of Friday evening a "vile and cynical act".

"We love and respect this Russia that gave the world many achievements and culture, but are concerned for this Russia where such killings happen," President Rosen Plenveliev has said.

The comment of Bulgaria's head of state was dedicated to the murder of opposition activist Boris Nemtsov who was shot dead last week.

Opposition leader Ilya Yashin has announced a rally paying tribute to Boris Nemtsov is to take place on Sunday, March 1, after a dispute with Moscow officials was settled.

Earlier, the municipality denied Nemtsov's fellow activists the right to reschedule a march which was planned to take place on Sunday, on the outskirts of Moscow. 

There have been various suggestions as to why opposition leader Boris Nemtsov was killed on Thursday evening in Moscow, 500 meters from the Kremlin. Here are some of them:

Dmitry Peskov, the Kremlin's spokesperson, has called the development a "100-percent provocation" and "a contract killing".

The opposition in Russia has rescheduled a march planned for Sunday after prominent politician Boris Nemtsov was murdered on Friday evening.

Alexander Chernykh, a member of Nemtsov's party RPR-PARNAS, wrote on Twitter that no protest action will be held in a more suburban Moscow area, but only in the city center.

Also, no protest demonstration is to be held, but only a mourn

Bulgaria strongly condemns the murder of the prominent Russian oposition leader and former Deputy PM Boris Nemtsov, the top Bulgarian diplomat Daniel Mitov has said.

Mitov has extended his condolence to Nemtsov's relatives in a statement dated Saturday morning.

Leaders across the globe have reacted to the events of Thursday evening when prominent Russian oppositioner Boris Nemtsov was killed.

US President Barack Obama condemned the "brutal murder" in a statement and urged a "prompt, impartial and transparent investigation" .

Police have found four vehicles that CCTV systems spotted at the time and place of Boris Nemtsov's murder.

Nemtsov was shot 4-6 times in the back and died shortly before midnight on Thursday as he crossed a bridge in the view of the Kremlin. The fatal wound came from a shot in the heart, RT has reported.

A manhunt is now underway.