LUCKNOW, Nov 26: The police suspect involvement of a Samajwadi Party (SP) MP and an MLA in Monday evening's bomb attack on a police van carrying undertrials in Gorakhpur. The attack, which left 20 people - including undertrials and policemen - seriously injured, has added another gory chapter to the history of political violence in eastern Uttar Pradesh.A blood-stained vehicle believed to have been used by the assailants has been recovered from the residence of the suspect Gorakhpur MP, Shubhawati Devi, and her brother-in-law Chandresh Paswan, who is a legislator of the same party from Bansgaon.The police have rounded up nearly 20 people, including Paswan's father. One of the arrested, Shakeel, has reportedly confessed that he was among the attackers.The police believe the attack was aimed at two undertrials Rakesh Yadav and Brahma Yadav, accused in the killing of Shubhawati's husband Om Prakash Paswan, who himself was an SP legislator and a historysheeter. Both of them, however, were not in the van which was attacked.According to a senior police official, "The attackers believed that both the accused were in the police van, but they had already reached the jail by that time."IGP, Gorakhpur zone, U K Bansal informed that the assailants had fled on "a red Tata Mobile, which was recovered from the residence of Shubhawati Devi in Raji Samera village". The officer said the accused were in the process of removing blood stains from the vehicle at the time, and "one of them was hurt in the cross-firing between the police and them".The police believe Chandresh plotted the attack on the van for killing the Yadav duo, but the plan backfired as the two were not in the vehicle.Om Prakash was killed in March last year when a bomb was thrown at a public meeting he was addressing in a village near Bansgaon, in Gorakhpur district. He had several cases registered against him at the time.Brahma Yadav and Rakesh Yadav were arrested from Patna for the attack, and confessed to the crime. Rakesh, incidentally, also has political connections, having contested as an Independent during last October's Assembly polls against Chandresh, and lost.The police believe Om Prakash's murder had been a fallout of caste violence in eastern Uttar Pradesh and Bihar areas.