Police arrested two Chechens on Tuesday on suspicion of involvement in the killing of American journalist Paul Klebnikov, who was shot in Moscow in July as he left the offices of the Russian edition of Forbes, where he was editor, a spokesman for the Moscow police said.

Police detained the two at a Moscow apartment and found a grenade and three weapons, including a type of pistol that police believe was used to kill Klebnikov, according to Pavel Klimovsky, the police spokesman. The gun is undergoing ballistic tests to determine whether it was the murder weapon, Klimovsky said.

The arrests fueled speculation that the killing was retribution for one of Klebnikov's books, "Conversations with a Barbarian," in which he argued that some Chechen separatists were longtime criminals who had opportunistically cloaked themselves in the ideology of Islamic fundamentalism.

The book, published in Russian in 2003, was based on 20 hours of interviews with Khozh-Akhmed Nukhayev, a former deputy prime minister in a Chechen separatist government. At a Moscow news conference in 2003, Klebnikov said that Nukhayev was "a man who is quite outspoken in narrating the establishment of the so-called Chechen mafia in Moscow" and noted that Nukhayev had used the word "barbarian" to describe himself.

Klimovsky said that the two detained Chechens, who were 25 to 35 years old, came to the attention of police because of suspected involvement in a number of other crimes, including a kidnapping. The police declined to provide further details about the men or the kidnapping.

"We are waiting to hear the details, but if indeed this progress is real progress, we are very pleased," Klebnikov's brother, Michael Klebnikov, said in a telephone interview from the United States. "At first glance, it seems there is more of a trail to follow. We want to be absolutely sure that the people responsible for ordering Paul's murder are apprehended and convicted, not just the shooters. But catching the shooters, if that's proven, is a huge step, and we would applaud the Russian government."

"Because of the nationality of the people involved, it's very important that this be more than just suspicion. There has to be evidence that links them to the murder," he added. "And the next question is: Who ordered the killing?"

A third Chechen was detained during the early morning raid at the Moscow apartment, but Klimovsky said he may be released.

The investigation is being led by the federal prosecutor general's office and the announcement of the arrests by Moscow police took some observers here by surprise. In a statement, prosecutors appeared to criticize the police for releasing the information, saying that it could harm the inquiry and that only prosecutors and their investigators had authority to release such information. A spokesman for the prosecutor's office declined to elaborate on the statement.

Klebnikov, 41, was born in the United States into a prominent Russian family that fled the country after the 1917 revolution. He was a crusading investigative reporter and editor at Forbes who specialized in the interplay among crime, big business and politics in the new Russia. After the fall of communism, he wrote extensively for Forbes about the country's new capitalism and most recently oversaw the compilation of a list of the country's 100 richest people, a sensitive subject in a country where new fortunes have often been built on dubious foundations. He launched the Russian edition of Forbes in April.

He had also written a critical biography of Boris Berezovsky, a Russian business leader wanted by Russian authorities on various fraud charges, who has been granted asylum in Britain.

Investigators, who have interviewed as many as 300 people and tracked the reporter's phone records, were pursuing a number of lines of inquiry, including possible Chechen involvement and the Forbes list, according to Klebnikov's brother. He said in an interview before the arrests that the Klebnikov family was regularly briefed on the investigation by Vladimir Ustinov, Russia's chief prosecutor, or Ustinov's deputy.

Klebnikov's family also met with Foreign Minister Sergei Lavrov in New York last week and expressed concern about the apparent lack of progress in the case, Michael Klebnikov said.

Journalism is a dangerous profession in Russia. Twenty-one reporters have been killed here since 2000, according to Reporters Without Borders, a French organization that monitors press freedom around the world. Klebnikov was the first foreign journalist in Russia to be the apparent victim of a contract killing.

Correspondent Peter Baker contributed to this report.

Paul Klebnikov, an American who founded the Russian edition of Forbes, was shot dead in July.