Two women and a man have now been detained over Kim Jong-nam's death at Malaysia's Kuala Lumpur International Airport on Monday.
The other female suspect held Vietnamese travel documents.
A still photo from airport CCTV, confirmed as authentic by police, showed one of the suspects in a white T-shirt with "LOL" across the front.
It is not clear if the IDs of the women arrested were genuine of if they were believed to be the alleged assassins.
South Korea's spy agency believes Kim Jong-nam was poisoned by two female North Korean agents.
The National Intelligence Service said on Wednesday that North Korea had been trying to kill him for five years.
Officials say the 46-year-old told medical workers he had been attacked with chemical spray before he died.
A post-mortem examination has been carried out by Malaysian medical workers but the results have yet to be released.
Kim Jong-nam was the eldest of North Korea's late leader Kim Jong-il, who was supreme leader of the secretive country between 1994 and his death in 2011.
He reportedly fell out of favour with his father when he was caught trying to enter Japan on a false passport in 2001, saying he wanted to visit Tokyo's Disneyland.
That episode and his several years spent living abroad were seen as damaging to his leadership potential.