Thai police issued arrest warrants Monday for two more suspects, a Thai woman and a foreign man of unknown nationality, as part of a widening investigation that yielded its first arrest over the weekend in connection with a deadly bombing in Bangkok two weeks ago.

Police spokesman Prawut Thavornsiri said he was certain the two were part of a group responsible for the Aug. 17 blast at the Erawan Shrine in central Bangkok that killed at least 20 people, more than half of them foreigners.

In a televised announcement Monday, Prawut displayed a photograph of the woman’s Thai identification card, showing her in a black headscarf, and a sketch of the man. He later said police were asking for additional arrest warrants.

Police said relatives of the woman, identified as 26-year-old Wanna Suansun, believe she is in Turkey.

The developments came after police arrested a man Saturday in an apartment in Bangkok’s outskirts and seized bomb-making equipment.

More bomb-making materials were discovered in a second apartment during a raid Sunday, Prawut said. He said the apartment, in a neighborhood known as Min Buri, was rented by Wanna Suansun, also known as Mai Saloh. He said the woman has a house registered in the southern province of Phang Nga. Police raided the house but did not find her.

Police Maj. Gen. Chalit Keawyarat said the woman’s relatives told police that she had been away for more than three months and that they thought she was in Turkey because her husband is Turkish.

“The relatives are trying to contact her so that she could prove her innocence to the police. The relatives believe she is not involved,” Chalit said.

No one has asserted responsibility for the attack, sparking numerous theories about who might have been behind it.

Speculation has grown that the suspect might be part of a group seeking to avenge Thailand’s forced repatriation of ethnic Uighurs to China in July.

Uighurs are related to Turks, and Turkey is home to a large Uighur community. The Erawan Shrine is especially popular with Chinese tourists, feeding the idea that it could be a target of those who believe the Uighurs are oppressed by China’s government. Beijing says some Uighurs are Islamist terrorists.

The suspect arrested Saturday had a Turkish passport, though Thai authorities say it was fake.

Other theories posit that the perpetrators are Muslim separatists from southern Thailand, opponents of Thailand’s military government or feuding factions within the security services.