Friends and colleagues of murdered journalist Pavel Sheremet demanded a proper investigation into his murder during the unveiling of a memorial in Kiev on Monday.
The award-winning Belarus-born journalist was known for his sharp criticism of the Kremlin and Ukrainian leaders.
He died on July 20, 2016 when a bomb planted in his car exploded during morning rush hour in Kiev, where he had long been resident.
Five suspects were detained in December over the killing, but there is growing discontent among Sheremet's supporters over the integrity of the investigation.
"We still do not know who ordered this murder and there is a great deal of doubt about the suspects," said Sevgil Musaieva, editor-in-chief of online news outlet Ukrainska Pravda, where Sheremet was a columnist.
"There is no reliable evidence they did it, and their lawyers have information that may indicate that the case was falsified," Musaieva told AFP.
Dozens of people at the unveiling laid flowers and lit candles in front of a stone monument depicting a crumpled sheet of paper inscribed with the slain journalist's name.
- Lacking 'irrefutable evidence' -
The five official suspects -- two women and three men -- are all veterans of Ukraine's war with Russian-backed separatists in the east of the country.
"There are lots of questions, and it is clear that this lie will fall apart in court," Mykola Orekhovsky, a lawyer for one of the suspects said during a press conference in Kiev on Monday.
President Volodymyr Zelensky on Monday demanded that investigators come up with "convincing, irrefutable evidence" of the suspects' involvement.
Zelensky wrote on Facebook that "Ukrainians and the whole world" need to see "the true murderers of Pavel Sheremet and then the true organisers of this crime."
The US embassy in Kiev said on Facebook that it was joining "Ukrainians who continue to demand a thorough, impartial and credible investigation".
Two of the five suspects are accused of physically planting the explosive under Sheremet's car: ex-serviceman Andriy Antonenko and Yuliya Kuzmenko, a military medic.
The two have already spent seven months in pre-trial detention, but their lawyers and supporters say they have been wrongly accused.
The three other suspects are not currently in detention. A trial date has yet to be set.