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Mr. Filin suffered burns to his face and eyes when a masked man approached him outside his apartment near midnight on Jan. 17 and flung a jar containing sulfuric acid at him. He has undergone a series of operations in hopes of preserving as much of his eyesight as possible and is receiving further treatment at a clinic in Germany.

Russia's Interior Ministry said in a statement that it was proceeding with "a series of urgent investigative actions," including questioning the suspect, who was detained in the Moscow suburb of Stupino, and searching his apartment.

A law enforcement official told Russian television that the man is suspected of carrying out the acid attack on a contract basis and not associated with the Bolshoi Theater. The official said investigators have not identified the person who ordered the attack.

Katerina Novikova, the theater's spokesman, said the announcement was good news and that the attacker would lead police to the crime's mastermind. She noted that Mr. Filin had been harassed for weeks leading up to the attack, with barrages of calls to his cellphone and hackers breaking into his personal e-mail.

"I am hopeful, because I know that the investigators have worked long and hard, and I am very glad that someone has been arrested," she told Ekho Moskvy, a radio station. "I hope this is the right path, and the crime will be entirely solved, because it is important to know everyone who stands behind this: behind the attack on the Internet, the telephone calls, and above all the act of vandalism which was carried out on the 17th of January against Sergei Filin."

Mr. Filin and Bolshoi officials have said they believed the attack was motivated by a professional grudge, and the weeks after the attack brought a deluge of commentary on behind-the-scenes power struggles at the ballet company.

There was particular scrutiny of the rancor between Bolshoi officials and the premier dancer Nikolai Tsiskaridze, who has been passed over for administrative positions in the past. Mr. Tsiskaridze said on Tuesday that the detention had come as a surprise and that investigators have not approached him since he was questioned immediately after the attack.

Vesti, a Russian news channel, reported that the police tracked the man down by checking the records of mobile telephone calls that were placed from the area around the attack.