At least four persons were killed and over a dozen critically injured after the roof of an under-construction building caved in here leaving as many as 50 persons trapped under the debris on Wednesday, police said.The six-storey building, located in Shivgodavari area, was owned by Samajwadi Party leader Mehtaab Aalam, a police official said.The police and a team of National Disaster Relief Force rushed to the spot. The army was also requisitioned to pull out the trapped persons.In a joint operation, two dozen people were pulled out of the debris and rushed to medical facilities.While four succumbed to their injuries, a dozen continue to battle death. Expressing sorrow at the loss of lives, the General Secretary of the BJP's Uttar Pradesh unit, Vijay Bahadur Pathak, accused the Akhilesh Yadav government in the state of turning a blind eye to illegal construction which imperilled the lives of innocent people."I am accusing the Chief Minister of not only protecting such people from his party but also of patronising them for benefits. The SP government cannot shy away from responsibility over the tragedy," the BJP leader said.