May 8: Amnesty International and Human Rights Watch jointly call for an impartial investigation, relating what was reported so far, with questions about police response and other issues. They put the onus on Kiev to be fair, and note their promise to work with experts from Europe and Israel.
May 12 - formation of May 2 Committee, a panel of civic leaders, journalists, and experts coordinated by social worker Sergey Dibrov. A May 19 report has Dibrov explaining (it seems) it wasn't to replace official investigations but to do their own work since people shouldn't just trust them. They planned to annoince their first findings in early June.
May 13: Announcement of "Temporary investigative commission" in the Verkhovna Rada (Ukraine's parliament) Something from the Ukrainian Rada (official site, Ukranian). It's co-chaired by a member of the Regions party and a member of the Fatherland party for balance, but the latter was allegedly involved in organizing the riots and massacre. MP from the Union "Fatherland" Alexander Dubovogo..." (as mentioned by MFA July 23) Interesting tidbit: " Ex-Head of the Odessa Police Dmitry Fuchedzhi accuses deputy from the party "Fatherland" Alexander Dubogovo (Александра Дубового) of organizing mass riots in Odessa May 2..." (Antimaydan Odessa)
June 15: UN Human rights report (PDF link) calls May 2 in Odessa "the most serious single incident of significant loss of life in Ukraine since the killings on Maidan," and noted that the government is blocking oversight of its dubious investigations::
...six official investigations have been established. The main bodies undertaking such investigations are the Ministry of Interior (MoI) and the State Security Service in Ukraine (SBU). It is with regret that the HRMMU reports a lack of cooperation from both governmental bodies, particularly at the central level with the HRMMU, which has been preventing the HRMMU from conducting a proper assessment of the progress made.
September 4: "On September 4 Chairman of the commission of the Odessa regional council Grigory Yepur said that the commission had disbanded itself. The investigation has been conducted by the Prosecutor's General and the Interior Ministry of Ukraine which are not accountable to deputies of a local level, Yepur said." (Itar-Tass, Sept. 8)
September 8: The Rada investigation, perhaps the best (official) chance at real insight, releases report. It instantly has one signatory withdraw her endorsement over significant changes she didn't agree to.See below and talk page.
Sept. 19: Considering Odessa alongside the February events on the Maidan in Kiev, Itar-Tass reported Sept. 19, the Council of Europe's international consultative group "agreed to broaden its mandate and to check whether (the investigations) meet international norms." They cited Daniel Holtgen, spokesperson of Council of Europe Secretary-General Thorbjorn Jagland, who said Kiev agreed to an expansion already on September 12. Itar-Tass notes this expansion could well stall the planned release of the group's final report from its original early 2015 deadline.
Sept. 25: Ukrainian Interior Ministry announces it has finished its investigation. "The Ukrainian Interior Ministry's Main Investigations Department has completed the investigation into the criminal case opened on the basis of the riots that took place in Odesa on May 2, Zorian Shkiriak, adviser to the interior minister, said." (Kyiv Post) On the same day, president Poroshenko announced an appeal to Russia to retrieve a suspect and "bring him to justice due to the riots," Kyiv Post also reports. The suspect is not a member of the radical mob that torced the Trade Union Hall and murdered its inhabitant, but police deputy Dmitri Fucheji, who merely enabled things, seems to be anti-Kiev, and fled to neighboring (pro-Russia) Transdnistria. Duetche Welle (Ukrainian) reported on the press conference, where Poroshenko showed "democracy and love for the press." On "the punishment of the enemies of the Maidan," the president swore the killers of Instytutska street - implicitly from the old government - would be made to pay.Asked about Odessa by Russian journalists, "the President recalled that the main suspect is a former senior policeman Dmitry Fucheji. The president asked Russia to hand him over; "we need that to ensure the investigation of this tragedy. Without him, it is not easy."