The investigation into the bomb explosion on Monday night would be conducted thoroughly, he said.

“We are investigating a total of 14 security cameras in the area to find the culprits. We have obtained something that cannot be revealed.”

He did say there were signs and some evidence that the May 5 incident could be linked to a January 1, 2007 blast in which three people were killed and many others injured.

However, he declined to say whether the recent blast was politically motivated.

An initial investigation by police concluded that the bombing was meant to cause a disruption, not kill people.

Srivara also referred to a bomb attack on April 5 in front of the old building of the Government Lottery Office, saying the investigation had progressed but he could not say when arrest warrants could be issued.

He said police investigation teams had done their best to apprehend the culprits in both cases.