The four are believed to have directed the murder plot, and are still at large, police say.
They evade tightened border controls by using an unguarded route to cross the Tumen river, sources say.
It remains unclear whether marble and granite are included on a list of banned exports under current United Nations sanctions.
After viewing nerve agent-tainted shirts worn by suspects, defense claims victim’s blazer is missing.
Use of illegally seized assets by North Korea likely to anger South Korea, while sanctions could make it hard for the North to export the textiles.
Chemist’s testimony offers strongest evidence linking defendants to the airport killing.
They go home with bright smiles and colorful clothes as UN sanctions force cancellation of their visas to work.
Witness also says he could not identify Kim’s body through a DNA sample from next-of-kin.
Judge denies defense’s request to include names of four North Korean suspects in court record.