I’m no lawyer, but I believe the phrase you’re looking for is “statute of limitations”.
Certain crimes have statutes of limitations. One that immediately comes to mind is rape, for example. A rape victim cannot prosecute a case against his or her rapist more than a certain amount of years after the crime has supposedly taken place. I don’t know what the exact rationale for this is, but I think it has to do with the strength of witness testimony and the effect that time has on a person’s memory.
But you’d be surprised how many crimes there are out there for which the statutes of limitations never expire. I’m pretty sure that murder falls in that category. Haven’t you ever heard of cold cases that suddenly warm up even decades after the fact when new leads come in, seemingly from nowhere? I think the police are even obligated to continue investigating under these circumstances.
I’m not following this STL case too closely at all, but I would imagine that if the accused are successfully prosecuted even in absentia, then a sealed arrest warrant can be issued that will essentially last forever. Lebanon doesn’t even need to apprehend the suspects. It could be 30 years in the future, one of them could be traveling through a European (or otherwise affiliated) airport, and he could be arrested right there and then, and he’ll be in the international detention/prison system for quite a while thereafter.
I do agree with you however that there’s something quite grotesque about spending all this time and money trying to identify Rafik Hariri’s murderers in Lebanon, while simultaneously making the argument that you can’t continue to count the dead in next-door Syria because it’s too dangerous to do so! It’s so abhorrently screwed up! But alas, I don’t want to hammer this point too aggressively because the last thing I want is for Lebanon to get sucked into the horrible, Syrian quagmire or for the Lebanese to bear an undue, sacrificial burden to solve their region’s largest and most intractable problems!