KYIV -- Dozens of Ukrainian human rights groups and civic organizations have called for the resignation of the country's top law enforcement officials after anticorruption activist Kateryna Handzyuk succumbed to wounds suffered during an acid attack.
In an open letter published by the Kyiv-based Center for Human Rights Information on November 5, 75 Ukrainian organizations said they were "outraged" by the state of the investigation into a wave of attacks against Ukraine's civic activists.
Handzyuk, who was known for her scathing criticism of police corruption, was doused with sulfuric acid outside of her Kherson home on July 31.
The 33-year-old activist died on November 4 in a Kyiv hospital where she was being treated for burns from the attack.
Five suspects, including a law enforcement officer, have been arrested for their alleged involvement, but the mastermind of the attack remains unknown.
The 75 human rights groups and civic organizations wrote in their joint letter that the attack against Handzyuk was meant to "intimidate" those who "rebel against decades of rooted corruption and organized crime."
The groups demanded "the dismissal of the leadership of the Kherson police," which they said "from the very beginning sabotaged the investigation into the attack."
They also called for the resignation of Prosecutor-General Yuriy Lutsenko and Interior Minister Arsen Avakov, saying they have "sabotaged reform of law enforcement agencies" in the country.
The offices of Lutsenko and Avakov did not immediately respond to the letter.
WATCH: Kataryna Handzyuk died six weeks after making an impassioned video from her hospital bed, in which she listed dozens of attacks on civic activists that police have failed to clear up.
A Kherson city-council member and an adviser to the mayor, Handzyuk had often accused local police officers of corruption.
She underwent 11 operations in Kyiv after sustaining severe burns to more than 40 percent of her body when an unknown attacker splashed sulfuric acid over her head.
The exact cause of her death was not immediately known, but some reports suggested it was a blood clot.
President Petro Poroshenko on November 4 urged law enforcement agencies to do "everything possible" to find and punish Handzyuk's killers, while the Interior Ministry said that Ukraine's Security Service (SBU) was now handling the investigation and working on "establishing who commissioned the crime."
"The death of this fearless civil-society activist must spur the Ukrainian authorities into providing a credible answer to the question on everyone's lips: who killed Kateryna Handzyuk?" Amnesty International's Ukraine director, Oksana Pokalchuk, said.
"This answer will only come through an impartial, effective, and transparent investigation, the type of which we have not seen in so many cases."
The attack against Handzyuk was one of the latest in a series of brutal assaults -- including shootings, stabbings, beatings, and chemical attacks -- against Ukrainian civil-society activists over the past year.
There have been at least 55 such attacks since the beginning of 2017, according to the Center for Human Rights Information and journalists at the independent Ukraiynska Pravda news site.
While there have been some arrests, nobody has been convicted for perpetrating or ordering the attacks, activists say.
Pokalchuk said the authorities "have so far chosen to focus on a few individual cases and ignored the wider pattern and numerous specific instances, but this must now change."
"These killers, potential and actual, will be stopped only by real actions, not virtual ones," reformist lawmaker Mustafa Nayyem wrote on the Novoye Vremya news site, saying the outpouring of condolences on social media wouldn't be enough.
"Whether they will continue to drench us with acid, slaughter us in doorways, and shoot us in the back in our own country depends on how and what we do now," Nayyem added.
His brother, Masi Nayyem, a lawyer representing Handzyuk's interests, told RFE/RL that the "very first thing" needed to bring Kateryna's killers to justice was political will.
However, he said he did not expect this to happen, as the person who ordered the attack is likely a law enforcement official tied to powerful politicians.
Meanwhile, National Police deputy chief Kostyantyn Bushuyev told reporters in Kyiv that he was "convinced" that the material provided to the SBU will allow the agency to find and prove the guilt of "those who hired the hitmen."