The legal escape route for Muhammad Rizalman bin Ismail has not been updated for more than 50 years.
The Malaysian diplomat's right to immunity was based on provision 29 of the Vienna Convention, which states, among other things, that diplomats must be free to perform their duties without threat of arrest, and have immunity from civil or criminal prosecution.
The genesis of the current convention can be found in the Congress of Vienna; a meeting of ambassadors from Europe who convened in the city in 1814-15 to help formulate a plan for long-term peace in the region after the Napoleonic wars.
"A lot of international law evolved through this congress; laws that were designed to stop countries from going to war," explains Steve Hoadley, associate professor of politics and international relations at the University of Auckland.
The laws established in 1814-15 were further refined in 1928 in Havana with the Convention Regarding Diplomatic Officers.
The present treaty was adopted by the United Nations in Vienna in 1961.
The right to diplomatic immunity is important, especially for diplomats who are posted to politically volatile countries.
"It is good for Western diplomats who are sent to slightly dodgy countries with less transparent justice systems," says Hoadley.
But he says the right to diplomatic immunity can create an uneasy relationship between international relations and domestic justice.
In some situations, illegal behaviour by diplomats is overlooked by the host government if there is the likelihood of conflict with the diplomat's home nation.
"Claims are often not carried out in the interest of wider relations with the other government involved," says Hoadley.
The New Zealand Government could have initially asked the Malaysian Government to waive Rizalman's right to diplomatic immunity, but as this did not occur, he was allowed to return home.
New Zealand would have been breaking international law if they had not let him leave - essentially taking him hostage.
Although the provisions of the Vienna Convention are simple in wording, they can be broadly interpreted.
Hoadley says the legal team involved in the current immunity would be looking for similar cases for precedents to help them determine the correct course of action.
In this case the Malaysian Government agreed to extradite Rizalman so he could stand trial in New Zealand.
The Vienna Convention is one of the most widely accepted international treaties, with 190 signatories as of April this year.
There have been no moves to change or modify the Vienna Convention since it was adopted in 1961.