Soekarno-Hatta International Airport Police released three South Korean citizens who had been detained after explosive-looking materials had been detected in their luggage.

The trio — two men and a woman — had arrived in Jakarta on a Korean Airlines flight from Incheon, South Korea, on Sunday night, Salahudin Rafi, spokesman for airport operator Angkasa Pura II, said on Monday.

They were set to board a Lion Air flight to Balikpapan, East Kalimantan, but security officials pulled them aside and searched their luggage after scanners turned up images of objects similar to detonators, chemicals and jumper cables.

“After we had an examination of their luggage, which appeared to contain 10 objects similar to detonators, they turned out to be dummies and not harmful at all,” National Police spokesman Insp. Gen. Anton Bachrul Alam said.

“They were going use them in a presentation at a coal company in Balikpapan — PT Multi Mikrotama Kimia,” Anton said, adding that police were going to summon coal company officials to testify that the materials were for demonstration purposes only.

“We haven’t named anyone as suspects here, but we want to know for sure about this case.”