Now for the "why"? I suspect she turned his advances down, and that was something he wasn't used to. Goes along with the 'anger management' problems discussed by a reporter.
If the culprit is the Van der Sloot kid, he looks like a cocky s.o.b.
Blood found in avn Sloot's car, and a sample sent to US for possible DNA match with Natalee's mother's blood. From pictures on tv, the van Sloot 'boy' is tall and powerful. There were three 'boys' there that night. They should all be arrested and charged with murder.