In criminal law, a guilty defendant is punished by either: incarceration in a jail or prison, fine paid to the government, or, in exceptional cases, execution of the defendant, also known as death penalty. Crimes are divided into two broad classes: felonies, that have a maximum possible sentence of more than one year incarceration, and misdemeanors, that have a maximum possible sentence of less than one year incarceration.
The notion that the threat of punishment will deter criminal conduct is based on the principle that human beings are rational. In practice, criminals are either impulsive (i.e., not rational) or believe that they will not be caught by the police. Consequently, the threat of punishment does not deter criminal conduct.
In criminal litigation, the burden of proof is always on the state. The state must prove that the defendant is guilty. The defendant is assumed to be innocent and he needs to prove nothing. There are, of course, exceptions.
If the defendant wishes to claim that he/she is insane, and therefore not guilty, the defendant bears the burden of proving his/her insanity. Other exceptions include defendants who claim self-defense or duress.
Furthermore, in criminal litigation, the state must prove that the defendant satisfied each element of the statutory definition of the crime, and the defendant’s participation, “beyond a reasonable doubt.” It is difficult to put a valid numerical value on the probability that a guilty person really committed the crime, but legal authorities who do assign a numerical value generally say “at least 98% or 99%” certainty of guilt.