"As a minister, I consider the crime to be resolved. We have proof concerning the criminals, who have died, to our sorrow," said Interior Minister Yuriy Smirnov.
He dismissed opposition claims that journalist Heorhiy Gongadze's death was linked to his criticism of the government.
"Knowing the situation in full, I can state that the crime has been resolved and that it has no political grounds. This is a purely criminal matter," Smirnov said, according to the Interfax news agency.
Gongadze, an Internet journalist who was an outspoken critic of alleged high-level corruption in Ukraine, disappeared in the capital Kiev last September. In November, a beheaded body believed to be his was found in the woods near Kiev.
An analysis of the body by Russian and U.S. experts confirmed it was Gongadze's.
The Ukrainian opposition has seized on the case to demand the resignation of President Leonid Kuchma, whom it accused of involvement in the killing.
Opposition activists cited audio recordings supposedly made by a fugitive presidential bodyguard that purportedly documented Kuchma and his top aides discussing measures to silence Gongadze.
On the tapes, a voice similar to Kuchma's was heard ordering officials to "deal with" the journalist.
Kuchma denied involvement, saying the tapes were doctored to put words into his mouth. He accused unnamed forces of trying to destabilize the former Soviet republic, which has come under fire for its human rights and press freedom record.
Kuchma's denials did little to stop opposition protests, which were joined by those generally unhappy with Kuchma's performance.
Alarmed by the political turmoil and sporadic violence, foreign investors and the International Monetary Fund froze investment and lending programs.
Street demonstrations have abated lately.
Smirnov said law enforcement agents found the slain bodies of two people who allegedly killed Gongadze, and a map locating the journalist's remains was also discovered when the bodies were exhumed.
"The two perpetrators have died and there were no organizers because this action was spontaneous and sudden," Smirnov said. The minister said those who killed Gongadze's alleged attackers "have been detained and are being kept in proper places," and that an underworld boss known by the nickname of Cyclops was believed to be involved in the case, but was unable to give further details.
It was not immediately clear whether the opposition, or the international organizations that have urged Ukraine to conduct a full inquiry into the case, would accept Smirnov's conclusions.
Andriy Fedur, attorney for Gongadze's mother, said Smirnov's statement was "improper" and premature, adding that the investigator in chage of the case could not confirm Tuesday that it was resolved.
Fedur said he was suspicious about Smirnov's claims that Gongadze was killed "without a motive and out of hooligan reasons."
People on the streets of Kiev voiced their skepticism over the minister's announcement.
"I don't think the government itself knows what truth is. Tomorrow they will be telling us something completely different," said Ekaterina, a student in Kiev who declined to give her surname. "Whatever they said, the poor man is dead."
This week, President Kuchma was quoted by Ukrainian news agencies as saying he believed the case was not politically motivated, noting that Gongadze was not a famous figure.
The United States, European Union and international human rights bodies have expressed concern about the lack of progress in the investigation, which has been marked by inconsistencies.
In its most recent assessment of human rights in Ukraine, the State Department said the government there "interfered with the news media and restricted freedom of the press; however, a wide range of opinion is available in newspapers and periodicals."
"During the 1999 presidential election campaign, government authorities interfered in the election process and stepped up pressure on the media through tax inspections and other measures," it read.
Gongadze's widow, Myroslava, and the couple's two daughters have left for the United States, where they received political asylum. Also granted asylum was Maj. Mykola Melnichenko, the ex-bodyguard whose supposed recordings were instrumental in igniting the scandal.
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