ALMOST exactly a year ago, on May 2nd 2014, two groups of protesters clashed in central Odessa. A heady post-revolutionary haze hung over Ukraine. A weak government had taken power in Kiev after the Maidan protests had forced President Viktor Yanukovych to flee the country. Russia had annexed Crimea and pro-Russian rebels were taking over parts of the eastern Donbas region. Odessa, with its many Russian-speakers, might have been next.

Masked pro-Russian demonstrators then opened fire, scattering the pro-Ukrainian crowd. The pro-Ukrainians regrouped and pushed back to Kulikovo Pole, where pro-Russians sheltered in the Soviet-era trade-union building. Molotov cocktails flew and the building erupted in flames, trapping hundreds inside. Elena Radzikhovskaya, a local history professor, went to search for her son Andrei, who had joined the protests. She called him but, she says, “A strange voice answered and told me, ‘Your son is dead’.” A year later, Ms Radzikhovskaya still wears black.

At least 48 people died in the clashes. Six were Maidan activists killed in the first skirmish; the rest were pro-Russians, most of whom died in the trade-union building. These events scarred Odessa, and provided prime propaganda for Russia. Many separatists fighting in eastern Ukraine today say May 2nd was the day they decided to take up arms. Maidan activists in Odessa retort that it saved the city from a worse fate. “May 2nd is our victory,” says Mark Gordienko, a local Maidan leader. As for those who died in the fire: “Screw them.” But the wounds still fester. “This is a post-traumatic society,” says Zoya Kazanzhy, an adviser to the governor. On both sides, she adds, “radicalisation is deepening”.

Clashing memories and an amateurish investigation have marred the healing process. Ukraine’s president, Petro Poroshenko, has called the inquiry “a test of justice for the law-enforcement organs”. Human-rights activists say they have failed so far. Nobody has been convicted on charges connected to May 2nd. There is no official list of the dead. The evidence collected is thin. Investigators searched the trade-union building for a mere six hours the day after the fire, and then left it open to the public. For 16 days it was looted and defaced. By the time police put up a permanent perimeter barrier, the crime scene had been irreparably compromised. The ensuing detective work was inept.

The most reliable inquiry has come from independent journalists in the so-called May 2nd group. Official organs are “incapable of bringing this case to a just end”, says Sergey Dibrov, one of the group’s investigators. Many see politics interfering with justice. Of 22 people now on trial, only one comes from the pro-Ukrainian side. As for the police, “The function of our law-enforcement agencies became corruption, not investigation,” says Mr Dibrov, noting that one witness asked to identify a suspect in a photo line-up was shown a picture of him alongside images of Ben Affleck and Bruce Willis.

The authorities have cracked down on pro-Russians in Odessa. A string of bombings of pro-Ukrainian groups have killed only one person, a bomber, but they have also put the city on edge. The security services claim to have foiled a Russian-led plot to launch a “Bessarabia People’s Republic”. In the run-up to the first anniversary of May 2nd, dozens were detained. On the day itself, thousands of soldiers and police were deployed around the city, reassuring some but rankling others. “They aren’t guarding us, they’re guarding themselves from us,” complained a mourner at the Kulikovo Pole memorial.

Most of Odessa’s pro-Russians have been arrested, driven out or frightened into silence. Billboards encourage residents to inform on everyday separatism. Yuri Tkachev, editor of Taimer, a pro-Russian website, declares that “the authorities are digging themselves into a hole by not letting these people and ideas express themselves in a safe form. It may then appear in a dangerous form.”

A parallel power structure has been built from Kiev’s Maidan movement. During the revolution, self-defence groups played a big role, but now their presence carries its own risks. Mr Gordienko half-jokingly calls himself a “patriotic pirate”, and speaks of an alliance with Odessa’s powerful criminal underworld against the pro-Russians. Groups like his have taken the law into their own hands. During a night patrol earlier this month, one team roamed the city in a silver SUV with spoof licence-plates reading, “Putin is a dickhead, la-la-la-la-la”. The vigilantes listen in to police radio and intercept calls, competing to arrive on the scene first. They claim to answer to themselves, the people and some vague notion of justice.

Yet for all their mutual hatred, the two camps share two sentiments: a love for Odessa and a deep distrust of all those in power. Pro-Russian activists, having seen the destruction in the Donbas, have a strong incentive to refrain from steps that could lead to all-out war. At the same time Maidan groups speak openly of their disappointment with the dithering new government in Kiev.

The regional governor, Ihor Palitsa, has drawn praise for his handling of the May 2nd anniversary, which passed peacefully, but he is a compromised figure because of his close ties with Ihor Kolomoisky, a powerful oligarch. The government’s failure to investigate and prosecute most of those responsible for the crimes of May 2nd, and its failure to deliver the Maidan revolution’s promises, may pose the greatest threat of all to Odessa. The kindling is stacked; it needs only a spark.