A manhunt has been launched for the two persons suspected of planting the bomb outside Delhi high court which killed 12 people and injured 75.

Confirming this, Delhi police said they have released the sketches of the duo -- one believed to be in his 50s and the other in his mid-20s.

"We may also release a third sketch depending upon the eyewitness accounts," one Delhi police official said. 

Police are also investigating whether the person who planted the bomb was among the injured. 

According to some eyewitnesses, a man clad in a white shirt and carrying a briefcase was seen in the queue in front of the reception of the high court complex on Sher Shah Road just before the explosion. 

Investigators said they were yet to ascertain whether there was a timer in the device.  Police are also searching for a stolen car that may have been used by the suspects in carrying out the blast outside the Delhi High Court. 

"We have a registration number which we think is fake," a senior police official said.  The National Investigation Agency, which has been asked to probe the blast, is also examining the material used in the explosion.