Nine people were killed and 84 wounded by a bomb blast on a commuter train on the same coastal track nine days ago also blamed on the Tigers. Police released a picture of the suspect, identified as Jatheesan Balasubramaniyam, from Wattala, a suburb north of Colombo.
A statement from the security media centre said police were seeking assistance from the public to arrest the suspect. It gave telephone numbers for the public to call.
At least 18 people were wounded when the bomb, suspected to have been planted by Tamil Tigers, was set off alongside a packed commuter train between the Wellawatte and Dehiwela railway stations just south of the capital.
The attack came a day after the Tigers accused the army of a mine attack inside rebel controlled territory in the north that killed six civilians, a charge the army has rejected.