BANGKOK — Thailand’s chief of police said Sunday that those responsible for the deadly attack on a Bangkok shrine last week “may have already fled” the country, apparently trying to lower public expectations that the main person being sought would be caught anytime soon.

“If the police are lucky, we may be able to arrest them,” Gen. Somyot Poompanmoung, the national police chief, told reporters.

Hamstrung by a paucity of evidence, the police have stumbled over false leads and complained that they lacked the equipment and technology to gain sufficient insights from the grainy security footage and other images they have gathered showing the man’s movements before and after the explosion.

The blast last Monday at the Erawan Shrine left at least 20 dead and created panic in Bangkok’s main shopping district. More than a hundred people were injured, including some who remain in critical condition.