you can get tester kits that will identify the majority of street drugs.
http://www.eztest.com/shop/
they're pretty cheap to buy and easy to use.
if inside the capsule there is both a liquid and a pill then it's probably a combination of drugs, maybe ghb with
amphetamines or mdma. i've never seen anything like that before, i'd think it easier to mix both substances together then put it in a capsule.
another thing you could do is ask a police officer, if these are going around on the streets then they've more than likely come in contact with them and would have had them tested.