Maybe it will be a jealous astronaut who decides to eliminate a rival in an orbital love triangle. Or maybe being cooped up in a spacecraft on an interplanetary flight will cause one crew member to flip out and finally lose it at a colleague's annoying nose blowing. Or maybe it will be a killing made to look like an accident, in order for a co-conspirator to collect an insurance policy back on Earth.
But sooner or later, it seems likely to happen, given humans' propensity for committing homicidal violence against one another all over the world. Somebody is going to commit a murder in space or on another planet or moon, and, when it happens, authorities will have to figure out how to catch the perpetrator and bring him or her to justice.
But it's not going to be easy. Investigating a murder in space would be vastly more complicated and difficult than probing a crime on Earth. And law enforcement agencies and courts may have to deal with tricky, complex jurisdictional issues that end up requiring negotiations among spacefaring companies. And until the laws are rewritten, judges will have to take statutes and legal standards that were developed to deal with murder allegations on Earth and figure out how to apply them to accusations of lethal violence in space.