MOSCOW (Reuters) - Russian opposition activist Ivan Skripnichenko died after being attacked by a man angry he opposed Vladimir Putin. Over a month later, nobody has been arrested, his family can t see his autopsy, and authorities say he probably died of heart disease. The assault on the 36-year-old father-of-two is one of a growing number of vicious attacks on opposition figures in the run-up to a presidential election in March which Putin, the incumbent, is widely expected to contest. Most activists do not believe that Putin or the Kremlin have a hand in the attacks, which have included caustic liquid being thrown in a victim s eyes, a car being set alight, and, in one case, an activist being bashed over the head with an iron bar. But critics say the way the authorities have handled the cases - it s rare for anyone to be arrested and a nationalist group which says its carries out such attacks openly boasts about its activities - shows that they are at best turning a blind eye, and at worst tacitly condoning the violence. Yulia Latynina, a journalist critical of the authorities, was forced to flee Russia this summer after having faeces thrown at her, her car torched, and noxious gas pumped into her home.  For her, Skripnichenko s death is part of a dangerous trend, and she has accused the authorities of losing control of the violent extremists responsible.  When you splash antiseptic in people s faces, pour shit over people, beat up activists, puncture their tires, or burn something, sooner or later someone will be burned alive or die in a fight,  Latynina said on her own radio show.  And that s murder.  According to Skripnichenko s family, an unidentified man accosted him late on Aug. 15 as he stood by a makeshift memorial to slain opposition leader Boris Nemtsov on a Kremlin bridge, a rallying point for government critics. Nemtsov had been shot dead on the same spot in 2015 by a Chechen gunman in one of modern Russia s most high-profile killings.  Don t you love Putin?  the man asked Skripnichenko.  Is Putin a girl that I should love him?  the activist parried. The man knocked Skripnichenko s cap to the ground, and, as his victim rose after picking it up, punched him hard in the face, breaking his nose. Skripnichenko hit his head on the pavement as he fell. His attacker then kicked him as he lay prone. Mikhail Silich, an activist who was with Skripnichenko at the time of the attack, confirmed the family s account. After the attack, Skripnichenko left hospital and told other activists he thought he would be OK. His family say he went to a different hospital a week later to get his nose reset, and began to feel unwell in the canteen. When he didn t come home that day, they phoned the next morning to be told he had died. His family and activists say the authorities are not investigating his death properly. Investigators have neither identified nor arrested Skripnichenko s attacker, have not opened a criminal case, and the dead man s family say they can t obtain his autopsy report. Citing procedure, Moscow s Investigative Committee, which is handling the matter, told Skripnichenko s widow Olga that she would need to wait 40 days to get such a report. The committee did not respond to a Reuters request for comment on progress in the case. Despite the attack taking place in sight of the Kremlin s  walls on the same spot where Nemtsov was gunned down two and a half years earlier, investigators say there is no CCTV footage. Ilya Novikov, the family lawyer, says that s hard to believe.  The cause of death is in question too. Investigators  preliminary conclusion was that he had died of heart disease.  Skripnichenko s sister Nastya says doctors who examined her brother said he did not appear to have suffered serious head wounds. Yet she is skeptical he died of heart problems and suspects the attack triggered problems that took time to unfold.   My brother never complained about heart problems,  she told Reuters, saying doctors had given him a clean bill of health in a check-up as recently as this spring.  My brother was into cross-country skiing, flew a glider, did parachute jumps, and cycled at a semi-professional level. I absolutely link my brother s death with the attack.  Russia s liberal opposition has no seats in parliament and  scant hope of mounting a serious challenge to Putin next year, though Alexei Navalny, an opposition leader who doesn t fit the traditional liberal mould, is trying to make a run.  But in a country under Western sanctions because of its 2014 annexation of Ukraine s Crimea and support for pro-Russian separatists in eastern Ukraine, pro-Kremlin politicians often cast anyone critical of the authorities as  the enemy within .  Critics say such rhetoric is fuelling attacks against the opposition and that those who carry them out feel a sense of impunity because they are rarely punished. Navalny became temporarily blind in one eye in April after having caustic liquid thrown at him. Soon afterwards, a pro-government TV channel broadcast footage of Navalny s attacker running away from the scene, but blurred out his face. Opposition activists identified the man as a member of a radical group; investigators said there was not enough evidence for a prosecution. In another incident, Nikolai Lyaskin, a Navalny ally, was hit over the head with an iron bar in Moscow last month, an assault Navalny said was designed to turn him into  an invalid.   Police detained a suspect and opened a criminal case, but they then issued a statement saying the suspect had told them that Lyaskin, the victim, had paid his assailant to stage an attack on him. Police released the suspect after 48 hours on conditions which were not disclosed. The spot where Skripnichenko was attacked is a favorite target for nationalists who dislike the makeshift shrine there to Nemtsov. For them, the former deputy prime minister turned Putin critic is a pro-Western traitor. They have sometimes trashed his shrine and picked fights with its defenders. SERB, a radical nationalist group, has vandalized the memorial several times. At an apartment block in Moscow where Nemtsov once lived, SERB s leader Igor Beketov tore off a plaque that activists had hung honoring Nemtsov. A state TV report about the incident complained the opposition was using Nemtsov s name  for various purposes  and gave Beketov air time to explain his grievances.   Outside the apartment block, Skripnichenko family lawyer Novikov became embroiled in a fist fight with Beketov after SERB members ripped up a photo of Nemtsov. SERB pelts its targets with faeces, antiseptic and urine. It has smashed cake into Navalny s face, but denies the caustic liquid attack. It has also hinted it threw faeces at Latynina.     Tamara Lugovykh, an activist who knew Skripnichenko, said she fears the authorities will do everything not to link his death to politics. In interviews with Reuters, seven activists said the attack chimed with the regular intimidation they face. They saw parallels with the investigation into Nemtsov s murder, which convicted a group of Chechens but failed to identify who ordered the killing and why.   Real blood has been spilled on the same spot a few meters apart,  said activist Andrei Margulev.  At the bridge shrine, a portrait of Skripnichenko is now on display next to that of Nemtsov.  Ivan had plans to have children with his wife,  Sergei Kireyev, an activist who knew him, said.   But anything can happen on the bridge. There are no rules.  
'No rules': Russian activist's death a symbol of pre-election violence