Wow. Apparently, unknown DNA traces were found on Teoh Beng Hock's clothes. And two guys refused to give samples of their DNA. Which, in CSI, would have immediately pointed out the killers early on and leave Grissom with only the method to solve.
My advice? Cooperate fully. Otherwise, avoiding it will at the very least ask awkward questions. And later on, they will get a court order for their DNA anyway. Or, just stand anywhere they are eating and then take away the glass or the fork and spoon as soon as they are finished. It's 'in plain sight'.
I doubt anyone is willing to be BleachMan and cover everything they've ever touched with bleach. Everything. Including their wives. And mistresses.
I would like to volunteer to give the Malaysian police my DNA, stool, blood and semen sample. Especially semen sample. You can have that anytime, man.