People with flags from many different opposition movements march in memory of Boris Nemtsov.

Thousands have marched in Moscow to mark the second anniversary of the assassination of outspoken opposition leader Boris Nemtsov.

Organisers estimate up to 15,000 Russians took part, but Russian police say it was closer to 5,000.

Boris Nemtsov was shot dead on a bridge near the Kremlin two years ago.

Five Chechen men are on trial for his murder, but his family say the real culprits who ordered the killing are likely to never be identified.

They want further investigations.

Several other outspoken opposition leaders have stepped up to take Nemtsov's place, but speaking out against the Kremlin is harder than ever.

Alexei Navalny was seen as the leading opposition candidate to take on President Vladimir Putin in next year's presidential election.

But he was convicted in early February of embezzlement in a trial widely regarded as politically motivated.

He was given a five-year suspended prison sentence, which put in doubt his ability to run next year.

Candidates cannot have convictions against their names, but Mr Navalny has vowed to appeal the ruling.

"On TV, they talk about enemies of Russia, but in reality, of course, there is this main enemy and he sits in the Kremlin," he told supporters at a Solidarnost meeting — a liberal democratic political movement founded by Nemtsov.

Share Alexei Navalny says Russia's main enemy sits in the Kremlin.

The ABC tried to question him at the meeting about how he planned to take on Mr Putin, but he refused to answer.

Organisers asked us not to question him in English in front of supporters — some believing that could be used against him by opponents.

The movement has also been rocked by the suspected poisoning of Vladimir Kara-Murza for the second time in two years.

The activist — also a friend of Nemtsov's — has now left Russia for further treatment in the US.

Share Five Chechen men are on trial for Boris Nemtsov's murder.

Opposition groups seen as weak, disparate

Ilya Yashin is one of the new generation of opposition leaders, and at 33, is realistic about the dangers.

"No-one is safe, of course we understand that. No-one is safe," he told the ABC at the Solidarnost meeting in a hotel on the outskirts of Moscow.

"After Nemtsov's murder many people were really scared, many people left the country, many people stopped their political activities.

"Because they thought if authority can kill a famous person, a celebrity like Nemtsov, the authority can do everything with a person like me."

Russia's various opposition groups are seen as weak and disparate.

"Oppositions look weak in every dictatorship because of pressure, because of police state, because of propaganda," Mr Yashin said.

"Changes will come not because of opposition and not because of opposition activities.

"Changes will come because of history. Changes will come because of justice."

He says there are more than 100 political prisoners in Russia.

Share Ilya Yashin says oppositions look weak in every dictatorship because of pressure.

Jailed in Siberia for one-man protest

Mr Putin signed new laws in July 2014 criminalising repeated street protests with a penalty of up to five years in jail — even if the protest is peaceful.

Anastasia Zotova's husband Ildar Dadin was arrested under that law.

He had been standing silently in Red Square with a sign — a one-man protest.

"The police said he came too often to these protests and he should be taken to prison and he is the only person arrested for that," his wife said.

"When he sees something illegal he feels like he should go to the Red Square and say he's against it.

"It's not like he wants people around him to see he's against it. He just does it for himself.

"He wants to be an honest human with himself."

Her husband complained of being tortured at one prison and was transferred to another one in Siberia, 4,000 kilometres away.

Share After Anastasia Zotova's husband Ildar Dadin was arrested under Vladimir Putin's street protests law, she feared he was dead.

She had no idea where he was for a month and feared he was dead.

"Putin says good things. In January, he said prisoners shouldn't be tortured, but his words mean nothing in Russia," she said.

"He said it for the public and the public was happy that our President was good but the torture didn't stop."

On February 26 this year, Mr Dadin was released from the Siberian prison after Russia's Supreme Court annulled his sentence.

Quiet walk to avoid arrest

Share Every Sunday afternoon, a group of protesters walk towards Red Square without carrying posters or chanting — to avoid being arrested by the police who follow them.

The law that enabled Mr Dadin to be arrested still exists, despite calls for it to be scrapped by human rights groups.

Other protesters are trying new ways to get around the restrictions.

Every Sunday afternoon, a large group of people congregate about 1.5 kilometres from the Kremlin and begin walking along the footpath towards Red Square.

Share Ildar Dadin has had his conviction overturned and he is now free, but the law that allowed him to be arrested still exists

They do not carry posters or chant. They simply walk.

Police follow them along their path, but technically they are not breaking the law.

I asked one of them why they had come out on a snowy Moscow Sunday when the temperature was minus 6 degrees Celsius.

He replied in English: "Society. Liberty. Society."