The Criminal Bar Association says courts could become clogged with historical crimes, as police seek to use new powers under Evidence Act amendments to get convictions in cold cases.
A 70-year-old Rotorua man was arrested on Friday and charged with murdering Raymond Tahu, who was shot dead at a Turangi petrol station in 1979.
Tony Bouchier, the president of the Criminal Bar Association, says the arrest creates a precedent that could potentially open up tens of thousands of similar cases.
Mr Bouchier says changes to the Evidence Act mean police can prosecute crimes of the 20th century under 21st century law.
He says people are entitled to closure on cases and reopening them would clog up the courts and may not best serve justice.
Mr Bouchier says the case has created much discussion in the legal fraternity and it will probably be fought to the top of the court system.
He says abuse of process is one of several potential grounds of appeal in cases such as this.