A statute of limitations is the period of time within an action must be brought to justice. This basically means if you commit a crime like theft, for example, you have to be caught within a certain number of years or you can not be punished. The statue of limitation varies by country, state, and crime.
In the United States there is no statute of limitation for murder. This is not true of all countries. Japan's statute of limitations for murder is 15 years for murders committed before 2005. Murders that occur after 2005 have a statue of limitations of 25 years. This only counts if your in the country. If you flee the country to not get caught, the time outside of Japan does not count. What this means is occasionally people have killed someone than after waiting 15 years they have confessed and they can not criminally punished (can still have a civil suit brought up against them though until 20 years for pre-2005 murders). Occasionally if you read Japanese newspapers you will read about a person who has managed to avoid the police for 15 years and got away with the crime. In Japanese detective drama's the 15 year mark shows up often. Some people have confessed and wrote a book or something about how they killed someone after the statute of limitations passed and the police can not do anything about it.
Some people are upset that there is a statute of limitations on murder. A lot of people really, a Mainichi poll says that 77% of Japanese people polled think that the statute of limitations on murder should be abolished. The statute was created more than a hundred years ago during a time when it was thought that a civilized country would have one. At the time this was true, British and USA didn't but a lot countries like Germany (no longer has one since after WW2) and France (now is set 10 years after the case closes) did. Some countries still do have them China has a 20-year limit on crimes punishable by death.
I can not find much information on Japanese statutes of limitations for crimes other than murder. I did find out that for theft, particularly art theft, the statute of limitations is two years. Which means if you have something stolen you would not be able to bring a claim for stolen property after two years. I also found out that robbery resulting in injury had a 10 year statute that was changed to 15 years in 2005.