Last Thursday afternoon Volodymyr Rybak, a city councillor in the east Ukrainian town of Horlivka, took part in a "flash mob" demonstration in support of the unity of Ukraine and then tried to raise his country's flag to replace the separatist Donbass Republic's rising-sun banner flying above city hall. A scuffle ensued and four men, one wearing military fatigues and a black balaclava, bundled him into a car; his telephone was switched off. On Saturday the body of a man thought to be Mr Rybak showing signs of torture – stab wounds to the stomach, bruises on the chest – turned up in a river near the separatist stronghold of Slavyansk, more than 50 miles away.

Sergey Bobok | AFP | Getty Images

After his wife Elena and son Yura travelled there to identify the corpse at the city's morgue on Wednesday, Ukraine's interior ministry confirmed this was indeed the slain politician, whose body was found with that of a second, still unidentified man. Mr Rybak's death adds to a growing file of vigilante "arrests" and disappearances of politicians, activists and journalists – blamed on armed separatists – as law and order erode, the civic fabric frays, and fear of violence grows in Ukraine's east. "The fact that people are disappearing in Ukraine – in the centre of Europe – in 2014 is simply horrible," Yurii Zhuk, a pro-European city councillor who saw Mr Rybak half an hour before his death, said on Wednesday, looking out the window of the city hall to the plaza – overlooked by Lenin's statue – where the abduction occurred. "It shouldn't be happening." More from the Financial Times:

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Oleksandr Turchynov, Ukraine's acting president, made reference to Mr Rybak's case on Tuesday evening when he accused "terrorists" in the east of torturing and killing "Ukrainian patriots", even as he announced plans to resume Kiev's suspended security crackdown on secessionist forces. The Donetsk-based website Novosti Donbass and the Kyiv Post newspaper on Wednesday published a list of 11 people kidnapped in Slavyansk and Horlivka over the past week. The list included Mr Rybak and Slavyansk's elected mayor, Nelly Shtepa, who disappeared last Friday after trying to meet the city's self-proclaimed "people's mayor", Vyacheslav Ponomarev. Journalists who have been detained include the American Simon Ostrovsky, whose work included vivid video reportage of the violent takeover of Horlivka's police station last week, and Ukrainian Serhiy Lefter, who was kidnapped by unknown people on April 16 while reporting in Slavyansk.