KYIV -- By all accounts, Ihor Humenyuk was a brave and selfless fighter against Russia-backed separatists in eastern Ukraine.
"We met in the thick of things, in [the village of] Pisky," recalls fellow volunteer fighter Volodymyr Nazarenko. "I'd say he was a brave and confident fighter who risked his life in some of the hottest fighting, including in Pisky near the Donetsk airport."
Now, however, authorities in Ukraine have accused the 24-year-old Humenyuk of throwing a grenade at security forces outside the country's parliament on August 31, killing three national guardsmen and wounding dozens more. It was an act that President Petro Poroshenko has described as "a stab in the back" to the entire country.
Humenyuk, 24, admits that he was at the fatal demonstration but denies that he threw the grenade, defense lawyer Sidor Kizin told journalists on September 1. Police officials, however, said that he admitted throwing the explosive under questioning and that another, identical grenade had been found during a search of his residence.
Humenyuk is a member of the Sich volunteer military battalion organized under the auspices of the ultranationalist Svoboda party. In a video posted on YouTube, he says that he served as a beat officer in the police, in addition to serving in combat in eastern Ukraine.
WATCH: Ihor Humenyuk Talks About Himself On YouTube (in Ukrainian)
"Before that I was a student and I actively participated in the Maidan," he says, referring to the 2013-14 pro-EU unrest that ousted former President Viktor Yanukovych. "I fought against the Berkut [riot police] on February 20 and was with the boys when the snipers were shooting. Then we went together into a volunteer battalion. I spent a year in the antiterrorism operation. We have been defending our mother Ukraine with weapons in our hands already for a year."
But now that he has been arrested, some of Humenyuk's comrades have been trying to distance themselves from him. In an interview with RFE/RL's Ukrainian Service, Sich commander Oleh Pisarenko said Humenyuk was a good soldier but that he had recently submitted his resignation from the battalion. Asked about the hand grenade from the August 31 demonstration, Pisarenko was certain it didn't come from his arsenal.
"Either it was some sort of war trophy or someone in Kyiv gave it to him," Pisarenko said. "I don't see any other possibility."
A spokesman for the Svoboda party, Yuriy Sirotyuk, told RFE/RL that Humenyuk was not a member of the party "on August 31." He noted that it is not legal for police officers to be members of political parties and declined to say whether Humenyuk was a Svoboda member before he joined the police force.
However, there are indications that Humenyuk was fairly prominent within Svoboda. He was featured in military uniform in a photograph that was part of the party's campaign materials for the 2014 parliamentary elections.
Also, under the pseudonym Ihor Dubenko, he appears in an online video promoting the patriotic youth organization Sokol. In another video, posted in December 2014, Humenyuk expresses the disenchantment that many Maidan activists felt when reforms did not come rapidly after Yanukovych fled the country.
WATCH: Ihor Humenyuk Dissatisfied With Pace Of Reform (in Ukrainian)
"You know what people say --- those who help the Maidan and took part in the Maidan," Humenyuk says. "They are all talking about being betrayed. Surely Yanukovych also thought he would be in power forever, that he could just spit on the people, that he has the Berkut and other units and would always be able to keep the people obedient."
"But it is not possible to keep our people in obedience," he continues. "That is why our government must always remember that we can tolerate a situation for a certain amount of time -- but at some moment we will burst. Everything is up to the government now."
The three victims killed in the August 31 bombing have been identified as Ihor Debrin, 25, Dmytro Slastniko, 21; and Oleksandr Kostina, 20. All three were National Guard conscripts.
Debrin, who celebrated his birthday on August 16, was buried on September 2. Kostina reportedly was married immediately before entering the National Guard.
Ninety other guardsmen and police were injured in the violence outside parliament on August 31.
RFE/RL correspondent Robert Coalson contributed to this report from Prague