Vladimir Putin is following the probe into the acid attack on the Bolshoi ballet\'s chief, his spokesman said Wednesday, after theatre staff signed a letter to the Russian president defending the dancer charged with masterminding the crime. \"Putin, like everyone, is following the investigation, but the investigation of an attack on a person is not the president\'s prerogative, it is the prerogative of law enforcement authorities,\" his spokesman Dmitry Peskov told Russian news agencies. The police detained Bolshoi soloist Pavel Dmitrichenko last week along with the suspected getaway driver and the perpetrator of the attack on Sergei Filin, which caused facial disfigurement and serious eye damage. Dmitrichenko admitted in court that he had asked the perpetrator to beat up Filin but said he had never intended the use of the sulphuric acid that the attacker flung in Filin\'s face. Filin has undergone numerous operations and is currently being treated in Germany. He will stay in Germany for a further two months for \"conservative treatment\", a Russian medical source told the Interfax news agency, saying that he is not scheduled for any more operations. The theatre\'s workers -- including dancers, choir and orchestra members and stage crew -- said in a letter to Putin and the government published online on Tuesday that Dmitrichenko\'s confession seemed forced. \"For everyone who knows Dmitrichenko, the very idea that he could have thought of and ordered this crime -- committed in such a brutal manner -- is absurd,\" said a copy of the letter published on the website of Moscow Echo radio. However police dismissed the letter on Wednesday, saying they were confident they had a solid case. \"We are convinced that those detained in the case were involved in this crime,\" Maxim Vanichkin, a senior police official, told the ITAR-TASS news agency. \"During our probe, we did not identify a single inconsistency in the evidence they gave.\"