“There is no clear trace of explosives at the site. Forensic tests are still ongoing,” Central Police Forensic Science Division’s chief Pol Maj-General Tawatchai Mekprasertsuk said yesterday.

On Monday night, a big bang was heard in front of the theatre and there were reports that two women were slightly injured.

“When we arrived at the scene, we found broken PVC pipes. These pipes were used to hold up an advertisement board,” Tawatchai said. “We have collected evidence at the scene for examination.”

“The results should come out within a day or two,” Tawatchai said.

Meanwhile, Deputy Bangkok Governor Pol Lt-General Amnuay Nimmano said the site was cordoned off to facilitate the work of police and officials.

“We have also given footage from security cameras in the area to police and the Joint Administration of Security and Order Maintaining for the Grand Palace,” he said.

The joint administration has been active in the area for seven months to ensure the safety of people as many have visited the area to pay respects to the late monarch, HM King Bhumibol Adulyadej

“Since the joint administration is in place, there were no violent incidents except the bomb blast that erupted in front of the old Government Lottery Office [on April 5],” Amnuay said. “So we hope people won’t panic.”

A source said yesterday that it was very likely that the sound was caused by another bombing, marking the second explosion in the area near Sanam Luang in less than two months.

“An IC [integrated circuit] timer was found about 15 metres from the theatre. This means the bombers might have activated a pipe bomb left in front of the theatre,” this source said.

The source added that the timer was similar to another found after the April 5 explosion.

“We believe the culprits behind the two incidents are the same. Bomb-makers behind the second bombing must have high expertise though. There are hardly any traces of explosives left,” the source said.

The culprits had not intended to kill anyone given the scale of the blast, according to the source.