New Delhi - Two prisoners escaped from India's most secure jail in New Delhi by digging a tunnel under a wall and scaling another in a daring dash for freedom, an official and media reports said Monday.The pair escaped on the weekend from Tihar jail, Asia's largest, in what appeared to be a carefully prepared prison break that authorities are still piecing together.One of the two, identified only as Faizan and Javed, who had been awaiting trial on burglary charges, was recaptured on Sunday and was being questioned."They escaped sometime on Saturday or Sunday. We will find out how they managed to escape. It is too early to say how and when they staged the jail break," Tihar deputy inspector general Mukesh Prasad told AFP.Prison guards raised the alarm on Sunday when they failed to show up for roll call. The pair had scaled a wall from one compound into another before digging under the perimeter wall and crawling through a drain, the Times of India and other local media said.Authorities ordered an investigation on Monday into how they managed to slip past scores of armed guards and electronic surveillance.The jail houses top militants, mafia, other gangsters and hardened criminals. But the prison is hugely overcrowded with more than 13 500 inmates at the end of 2013 despite a maximum capacity of just 6 250.Earlier this month, India's National Human Rights Commission asked Tihar authorities to explain media reports that 18 inmates had been murdered in just in one month by powerful gangs running the place.