The head of a local rights group, Zainabitdinov was outspoken, condemning the crackdown as "genocide" and giving a far higher death toll than the government's figure of 169 people.
Then, on 21 May, Zainabitdinov went missing. Two days later, his family learned what had happened.
"The lawyer, his lawyer Mavluda Akhmedova, told me about it," explained Zainabitdinov's son, Ilhomjon. "She said he was detained temporarily. He was in Osh [in Kyrgyzstan] two days ago and was arrested. They told me to come [on 24 May at 9 a.m. I asked them about [reasons of arrest]. They didn't respond and told me to come tomorrow."
Zainabitdinov is one of the most prominent activists to be arrested in the wake of the violence in Andijon.
But he's by no means the only one.
That's according to local and international human rights activists, including the U.S.-based Human Rights Watch (HRW), which today highlighted Zainabitdinov's case.
"We're getting other allegations of human rights activists being detained, interrogated, beaten and so on," said Aleksandr Petrov of Human Rights Watch.
Petrov cited another recent example from Andijon -- two members of the human rights group Ezgulik (Goodness) reportedly beaten as they were on their way to interview witnesses of the 13 May violence.
Petrov said these and other cases are an attempt by the authorities to intimidate activists into silence.
"In the conditions that exist now in Uzbekistan and especially in Ferghana Valley, of course the authorities do their best to prevent all information coming out from that region and to prevent international reaction to the killing of hundreds of innocent people on 13 May," Petrov said. "That is, all those cases of harassment, detention and arrests, are the result of activities of local human rights activists to get that information, to get those testimonies and convey it to an international forum, international journalists and international human rights organizations and foreign states."
There are reports from other regions, too.
In Jizzakh, authorities reportedly summoned several activists to meetings with local officials, including the city's chief prosecutor.
Oktam Pardaev, the local head of the Independent Human Rights Organization of Uzbekistan, described the conversation at one of these meetings.
"I was threatened, and told, "Think about your family, you're still young. After you die, nothing will help you. Neither [opposition party] Erk nor money will help you,'" Pardaev said.
And in Namangan, local human rights activist Sobitkhon Ustaboev was arrested on 22 May.
Authorities acted after he announced publicly he would go on hunger strike to protest the killings in Andijon and the government's refusal to allow an independent probe.
"Instead of promoting economic reforms the Uzbek government is again repressing people, arresting people in order to silence their voices," said Olimjon Yunusov, another rights activist in the city. "If we continue to be silent the repressions will increase."
HRW said it is extremely concerned for the safety of Zainabitdinov and called for his immediate released.
The organization said the international community must call on the Uzbek government to ensure his safety -- and the safety of other activists.