I don't understand: why artificially create a set of deadlines before which one crime or another can be brought to the conviction stage? Why not be able to investigate and prosecute for an indefinite period of time after a crime has been committed? Why encourage criminals to just sit out?
Slightly going offside here
However, I should note that you don't need going back that far to show how it can be a problem. Just imagine that a police office knocks your door right now and hands you a citation because you got identified as the author of a robbery that happened two months ago in a nearby city.
You probably would be sure not to have performed that, but you would likely struggle to prove that. If you are lucky, it would have been at a time where you were working at your office or the gym, and not only would you know that at that time you would have been there, but there would also be records -and hopefuly footage- showing you there, as well as coworkers able to testify that (or, more likely, that they don't remember you not being there).
Otherwise, you would be having a hard time. Maybe you stayed at home? Could you get a witness that you didn't leave it? Even for other people that live there with you, perhaps you did unattended a short trip to the supermarket in which you would have had time to do the robbery? Or maybe you went to a shop, or just walking, where a security camera would identify you not being away. However, could you remember the path you followed and thus the recordings that need to be verified?
And that's just in a couple of months. Obviously if you knew in advance you would need it, you would remember every step, actually, you would have made sure to have an alibi. But if this day was no special for you, you had no reason to remember its details. A real probatio diabolica.
It is obvious why the burden of the proof must lie on the accusation. And even if finally everything resolves happily, a misguiding identification could result in a long and slow process to get out of.
Obviously, the longer a lawsuit can be filed against you, the longer you would have to preserve any relevant evidence if you are serious.
For instance, until Check 21 was passed in 2004, US banks needed storing the received physical checks many years, as there could be a claim about them. About 70 billion cheques were written annually in the US by 2001, according to Wikipedia citation of The Future of Money. You can imagine the giant warehouses they needed just to store used checks. All those requirements mean costs, and thus money. If there is a statue of limitations on a claim for a forged check, the bank would only have needed to store checks for that amount of time (nowadays, they store it electronically, but although a big improvement, still amounts to enormous disk space space requisites).
Statutes of limitations go back a long way
The law code of ancient Athens had a five year limitation period except for murder and constitutional crimes. According to Demosthenes, these restrictions were introduced to control sycophants (people who made their living as professional litigators) from bringing unjustified lawsuits in the hope of a lucky verdict.
- a plaintiff or prosecutor with a valid case should pursue it with diligence,
- the older the claim or allegation, the more likely evidence is to be unreliable or lost,
- litigation or prosecution of a long-past wrong may result in more cruelty than justice.
Obviously, this is all a matter of degree and different causes of action have different limitation periods.
Most civil causes of action have a limitation period of a few months to a few years which runs from when the plaintiff should have become aware (or from when they attain their majority if they were a child) that they suffered damage. The logic here is that people doing their normal day-to-day activities should not live in perpetual fear that someone from the distant past is going to come out of the woodwork to sue them over an incident they can't remember happened if indeed it did happen. Notable exceptions include claims for damage for child abuse which have a much longer limitation period if they have one at all.
Minor criminal offences usually have a very short limitation period partly as a spur to efficiency by those required to prosecute them and partly because the punishments are small and courts have better things to do with their time then try and sort out the probity of 15-year-old evidence for a speeding offence.
Serious crimes like, murder and sexual assault typically have no statutory limit or they have a limit that can be set aside on application to the court.
For example, in New South Wales the default limitation for civil matters is 6 years, however, it is only 1 year for defamation but 12 years if the action is founded on a deed (among other exceptions). For criminal matters, summary offences (magistrate's court jurisdiction and maximum 2 years imprisonment) must be must generally be brought within six-months, however, there is no limit on serious indictable offences.
For example, I might have a perfect alibi that proves I did not commit some specific crime. If twenty years from now I’m accused of this crime, I would have completely forgotten about the alibi, the witnesses seeing me in a different place would have forgotten, and only in the rarest situations would they remember the date.
So having a fair trial would be very difficult, since I cannot defend myself after that long a time. If I actually committed some crime around that time, but not the one I’m accused of, I might not even remember for sure whether I committed the crime or not.
Let's say that at the age of 21, you go and do something stupid, but aren't charged with anything. 25 years later, you run for President. Do you think a prosecutor should be able to haul you in for that decades-old crime?
If it was, say, a murder, then the answer is yes. But what if it were more like a drug crime that they can only prove because you give some excuse about not inhaling at a press conference?
why artificially create a set of deadlines before which one crime or another can be brought to the conviction stage?
It doesn't have to be brought all the way to the conviction stage in that time frame. It only has to be charged. It's not a violation of the statute of limitations if the trial happens to go past the limit.
Why encourage criminals to just sit out?
I'm not quite sure what you mean by that. But if an alleged criminal goes into hiding or leaves the jurisdiction, the statute of limitations generally "tolls" until they stop hiding or come back.
In the United States in particular, the sixth amendment guarantees an accused criminal the right to a "speedy and public trial". A statute of limitations is a way of defining what "speedy" means in a certain context.
A big reason this exists is to protect the defendant against a number of abuses such as:
- Arresting a suspect, detaining them in jail until their trial, and postponing the trial indefinitely. This effectively denies them of their right to a trial, plus it enables the state to give an effective life sentence for petty (or imagined) offenses. This practice was one of the complaints that the American colonists had about the English justice system at the time.
- After a crime is committed, the state gathers a large amount of evidence but waits many years to charge the suspect. Since the state already has their evidence, they can wait to arrest the suspect until the suspect's witnesses have died, memories have faded, or it becomes otherwise impossible for the suspect to defend himself. This denies the suspect the ability to make a reasonable defense, heavily tips the scales in favor of the state, and increases the likelihood of a wrongful conviction.
- Causing undue harm to an innocent person. Charging someone with a serious offense causes their social standing, personal relationships, and professional life to suffer. A speedy trial means they can quickly clear their name. If trials could be postponed indefinitely, a falsely-accused person could end up losing their business and friends and ruining their life before they were ever able to defend themselves. It's bad enough when this happens accidentally, but it can also be used as a weapon against political enemies.
Statues of limitations don't just benefit the accused, they also have benefits for society in general and for the state:
- A criminal is likely to commit another crime so long as they are still free. Arresting and trying them quickly means you are protecting society against further offenses. Giving prosecutors a deadline is a good way to ensure that they are aggressively pursuing offenders.
- The state has to provide for the accused while they are in custody. A long-delayed trial can mean the suspect is held in custody for an extended period of time, which can get expensive for the state.
- Long delays before trials make it more likely that courts end up with an enormous backlog of cases that they can't reasonably work through.
There's a good explanation (with sources) of the historical background of the "speedy trial" clause on congress.gov. Non-US jurisdictions may not have a "speedy trial" clause, but the overall motivations for statutes of limitations still hold.