Police on Wednesday filed for the pretrial detention of two suspects accused of vandalizing the walls of the historic Gyeongbok Palace in central Seoul with graffiti.

The Seoul Jongno Police Station said it is seeking to remand a 17-year-old male suspect, identified by his surname Lim, for repeatedly spraying the phrase "free movie" in Korean and the name of an illegal streaming site in the early hours last Saturday.

Lim's alleged accomplice, a 16-year-old female surnamed Kim, was released late Wednesday in consideration of her age and degree of involvement.

Lim and Kim testified that they had vandalized the walls of the state-designated cultural heritage site after an unidentified person offered them money through social media, claiming to have received 100-thousand won, or around 77 U.S. dollars, in advance.

Police have expanded the scope of the ongoing investigation to confirm the existence of a mastermind behind the crimes.

A third suspect, a man in his 20s accused of a copycat crime the following day, is awaiting a warrant hearing.