English idioms relating to law and order.

Above board	If a situation or business is described as above board, it is open, honest and legal. "There are no secret negotiations. Our dealings have always been above board."
Ambulance chaser	This terms refers to a lawyer who finds work by persuading people injured in accidents to claim money from the person who caused the accident. "Peterson & Scott are well-known ambulance chasers - that's how they make money!"
An accomplished fact (also: 'fait accompli')	Something that has been done or completed, before those affected by it can intervene or change it, is called an accomplished fact.
Arm of the law	This expression refers to the extent to which the authority or power of the law extends. "He fled to South America hoping to escape the arm of the law."
Behind bars	Someone who is behind bars is in prison. "If you hang around with that gang, you'll find yourself behind bars in no time."
Beyond any reasonable doubt	This is a legal expression which means that something is certain. "The court established, beyond any reasonable doubt, that the man was innocent."
In black and white	To say that something is in black and white means that there is written proof of it. "It's an obligation. It's written in black and white in your contract."
Blow the whistle	If you report an illegal or socially-harmful activity to the authorities, and give information about those responsible for it, you blow the whistle or you are a whistle-blower. "He refused to blow the whistle on his boss for fear of losing his job."
Breaking and entering	This term refers to the fact of entering a building or home illegally by breaking open a window, door etc. "The two men were found guilty of breaking and entering."
Have a brush with	When you have a brush with something, such as the law , you encounter or experience it briefly. "He had a brush with the law for speeding several years ago but has had a clean record ever since."
Burden of proof	The burden of proof is the necessity imposed by law to prove that what one says is true. "The burden of proof lies with the claimant."
Case in point	This term refers to an example which serves to illustrate, support or prove a point which is currently under discussion. "The latest incident is a case in point for the parents' association."

Catch somebody red-handed	If a person is caught red-handed, they are caught while they are doing something wrong or illegal. "The police arrived as the burglar was leaving the house. He was caught red-handed."
Caveat emptor	This Latin expression, which means 'let the buyer beware', is a warning to customers that goods are for sale "as is". The buyer is purchasing the articles at his/her own risk and is responsible for examining them beforehand. "Caveat emptor is a principle to be remembered when buying second-hand goods."
Crack down on something	If the authorities decide to crack down on something, they enforce the law by taking severe measures to restrict undesirable or criminal actions. "Following the increase in road accidents, it was decided to crack down on speeding."
Cut someone some slack	If you relax a rule, treat a person less severely or allow someone to do something which is normally not permitted, you cut them some slack. "Our parents are very strict; I wish they'd cut us some slack now and then."
Daylight robbery	The term 'daylight robbery' is used when the price of something is thought to be much too high. "$10 for an orange juice? That's daylight robbery!"
Fair hearing	When accused of wrongdoing, if someone gets a fair hearing, they get an opportunity to present evidence or give their side of the story, usually in court. "I can guarantee that you will get a fair hearing."
False pretences	If you obtain something under false pretences, you deceive others by lying about your identity, qualifications, financial or social position, in order to obtain what you want. "She obtained the interview under false pretences."
You can't fight the city hall	This expression means that it is useless to try to win a battle against a politician, establishment or bureaucracy in general. "Tom decided it was a waste of energy trying to obtain a tax refund - you can't fight the city hall!"
Get out of hand	If a person or a situation gets out of hand, they cannot be controlled any longer. "During the student demonstration, things got out of hand and several shop windows were broken."
Hit and run (accident)	When the driver of a vehicle hits another vehicle without stopping to provide help, identification or insurance, and fails to report the accident to the police, the collision is called a hit-and-run accident. "A hit-and-run accident deserves serious punishment. "
In trouble with the law	If someone is in trouble with the law, they are being questioned by the police in connection with something illegal or criminal. "The suspect has often been in trouble with the law."

A law unto themselves	If someone is a law unto themselves, they do things their own way and ignore what is generally considered as acceptable. "They're against discipline and allow their children complete freedom - they're a law unto themselves."
Lay down the law	Someone who lays down the law tells people very forcefully and firmly what to do. "The volunteers helped in a disorganized way. They needed someone to lay down the law."
Licence to print money	This expression refers to an officially authorized activity which enables people to make a lot of money without much effort. "The contract to supply computers to schools was a licence to print money."
Murphy's law	Referring to Murphy's law expresses a sentiment of bad luck and the idea that if anything can go wrong, it will. "We've tried to prepare for every possible incident, but remember Murphy's law ..."
Not have a leg to stand on	To say that someone doesn't have a leg to stand on means that they can't prove what they say. "Three people testified against him. He didn't have a leg to stand on."
Null and void	Something which is null and void has no legal force or is invalid. "The contract was declared null and void."
Paper trail	If a person or organisation leaves a paper trail, they leave evidence in writing or in document form that will serve as proof of their actions. "The police found a paper trail which lead to the author of the hoax."
Partner in crime	A person who helps you to plan something dishonest or unlawful is called your partner in crime. (This expression can be used jokingly as in this example.) "Sam was my partner in crime. He hid my son's new bicycle until his birthday."
Pervert the course of justice	If a person perverts the course of justice, they tell a lie or prevent the police from finding out the truth about something. "The suspect was accused of trying to pervert the course of justice"
Put one's house in order	If you put your house in order, your organize your own affairs or improve your methods before criticizing others. "The government should put its own affairs in order before telling other countries what to do."
Rough justice	Treatment or punishment that does not seem fair, or is too severe, is called rough justice, especially if it is not legal. "The way the player was treated by the media was very rough justice."
Sharp practice	Trying to achieve something by using underhand, deceitful or dishonourable means that are barely within the law or bordering on dishonesty is called sharp practice. "The company is under investigation for sharp practice so it's better to avoid dealing with them."
Signed, sealed and delivered	When an agreement, contract or treaty is signed, sealed and delivered, all the legal documents have been signed. "It is hoped that the agreement will be signed, sealed and delivered before the end of the week."
Smoking gun	A smoking gun is a piece of evidence or the indisputable sign of someone's guilt. "The fingerprints the thief left on the door-handle was the smoking gun that enabled the police to arrest him."
Take the law into one's own hands	If, instead of calling the police, you act personally against someone who has done something wrong, you take the law into your own hands. "Instead of calling the police, he took the law into his own hands and confronted the youth who had stolen his son's scooter."
Toe the line	If a person toes the line, they obey the rules and accept the principles of a person, group or organization. "If you want to stay in this school, you'll have to learn to toe the line."