The Principle of Presumption of Innocence is generally worded: “the accused is presumed to be innocent until it [that person] has been declared guilty by a court”.
Under these circumstances in the United States (and many other democracies throughout the world), the burden of proof lies with prosecuting lawyers who must convince the court system beyond “a reasonable doubt” with regards to the guilt of the accused. Defense lawyer, who act on behave of the accused, are not required to prove anything with regards to their client. However, the defense team will usually present evidence to show there is “a reasonable doubt” concerning the guilt of their client.
In Canada, section 11(d) of the Canadian Charter of Rights and Freedoms: "Any person charged with an offence has the right ... to be presumed innocent until proven guilty according to law in a fair and public hearing by an independent and impartial tribunal."
In France, article 9 of the Declaration of the Rights of Man and of the Citizen: “Every man is supposed innocent until having been declared guilty.”
The United Nations General Assembly, in its Universal Declaration of Human Rights, article 11, states: “Everyone charged with a penal offence has the right to be presumed innocent until proved guilty according to law in a public trial at which he has had all the guarantees necessary for his defence.”
The European Union (Council of Europe), within its Convention for the Protection of Human Rights and Fundamental Freedoms, says: “Everyone charged with a criminal offence shall be presumed innocent until proved guilty according to law.”
In the United States, the presumption of innocence is widely held within the legal profession to stem from Amendments Five, Six, and Fourteen of the Constitution of the United States.
Thank you to Wikipedia.com for its sources and references.