Kanpur, July 7 : The case of a letter, purportedly written by slain circle officer Devendra Mishra (who was killed in an ambush by gangster Vikas Dubey on Friday) apparently exposed the nexus between suspended police officer Vinay Tiwari and the gangster, and it is getting curious by the hour. The letter was released on the social media, allegedly by an IPS officer, and it did not bear the number or the date that is mandatory for all official letters. The IPS officer, later, even sought an inquiry into the letter. None of the officials, till late on Monday, agreeed to comment on the veracity of the letter though IG Kanpur Mohit Agarwal said that he would probe the matter. On Monday night itself, it was said that the letter is not traceable and efforts would be made to locate it. The letter, if found and verified, could prove to be damning evidence against policemen who helped the criminal and even tipped him off about the raid which led to the killing of eight police personnel. The undated letter was reportedly written three months ago by Devendra Kumar Mishra, the Deputy Superintendent of Police (DSP) who was shot dead in the ambush by Vikas Dubey and his men. He had addressed it to the then Kanpur SSP Anant Deo Tiwari. Tiwari is now DIG STF and is probing the Kanpur incident. The officer had complained in it about policemen helping the gangster, especially Vinay Tiwari, the police officer in charge of the Chaubeypur police station, who is now under suspension. Mishra had reportedly accused Vinay Tiwari of helping the criminal and shielding him against any possible police action. The letter called for strict action against the police officer. SSP Kanpur Dinesh Kumar Prabhu, said: "I am aware that such a letter is viral on social media. The preliminary search was conducted at the DSP's office and the offices of the Kanpur SSP (Senior Superintendent of Police) dispatch and receiving section. So far there are no records of this letter and we have found no file. But we are looking at it with more details." Meanwhile, an audio clip of a conversation between the slain DSP and the then SSP is also going viral in which Mishra can be heard complaining to the then SSP about Vinay Tiwari. Anant Deo Tiwari takes Vinay Tiwari on a conference call and can be heard pulling him up for not reporting to the circle officer-Devendra Mishra. Mishra led a team of 50 policemen from three police stations in a raid to arrest Vikas Dubey in an attempt to murder case. Dubey is charged in 60 cases including murder, kidnapping, extortion and rioting. When the policemen approached the village early on Friday, they were fired upon from rooftops. Vikas Dubey was allegedly alerted to the raid by policemen and was ready with an armed gang to attack the police. Four policemen have been suspended on suspicion of links with the criminal after call records of more than 100 policemen were scanned after the killing. Four days after the ambush, Vikas Dubey has still not been arrested by the UP police. On Monday, the bounty on him was raised to Rs 2.5 lakh. Three more persons in the Bikru village where the ambush took place were arrested late on Monday night. Meanwhile, the entire Chaubeypur police station which is under suspicion has been taken off duty and 10 policemen form other police stations have been posted there. Lucknow range IG Laxmi Singh reached Kanpur on Tuesday and will investigate the role of police personnel in the case and also. /IANS