Assessing reasonable grounds to suspect

Whether there were “reasonable grounds to suspect” the commission of an offence can be controversial. Recently our Court of Appeal has divided over whether there were reasonable grounds to suspect that the defendant had possession of an offensive weapon. The case is not yet publicly available, but suppression orders have lapsed. For people who have access to the databases the neutral citation is [2017] NZCA 108. When it is available it should be obtainable at nzlii.org (as number 108 in the list).

Reasonable grounds to suspect that a weapon will be found are required by s 27 of the Search and Surveillance Act 2012. Relevant matters were that it was 3 am when the defendant was questioned on a street and his response was “very cagey” as to where he had come from and why he was in the street and not wearing shoes although it was cold, his clothing (shorts and a camouflage jacket) was similar to that of a person who was believed to be involved in stealing from cars, he kept his hand in his jacket pocket and was behaving in an agitated manner (at [17]). These circumstances where held to have given the officer reasonable grounds to suspect that the defendant was in possession of an offensive weapon. Peters J (who delivered the Court’s judgment) recorded her dissent on this point. She did not consider that the circumstances relating to the initial dispatch to the scene suggested violence or a person with a weapon, and although the defendant was agitated nervousness is insufficient, and the defendant had simply kept his hand in his pocket. Further, he had identified himself, and there was nothing to suggest that he was going to use violence, particularly as four constables were present at the time of the search (at [26]).

The difference between the judges may be due to what assumption was be made at the beginning of the analysis. Should the defendant be assumed to have the probability of carrying a weapon that a randomly chosen person would have, or a randomly chosen person of the defendant’s age, and gender (to mention the two morally acceptable groupings), at that time of night? To avoid exaggerating individual facts which will be considered later in the analysis, the most neutral starting point should be chosen: the probability that a randomly chosen person has possession of a weapon.

However, another starting point sounds as if it is fair, but it will often lead to the opposite conclusion. This is that the defendant is just as likely to have a weapon as not to have a weapon. The even balancing here sounds neutral, until one asks, why should the defendant be assumed to have a probability of 0.5 of having a weapon? It may be that only 2 people out of every 100 have possession of weapons, so why not start with a probability for this defendant of 0.02?

Having chosen a starting point, the particular circumstances are examined. The judges may well have agreed on the probative value of each item and on the effect of taking them all into account together. Suppose that they agreed that the occurrence of these combined circumstances was 14 times more likely if the defendant had possession of an offensive weapon than if he did not. A judge who started with an assumption that the defendant was no more likely to have a weapon than would a randomly chosen person, would conclude that the ultimate probability that he had a weapon was around 0.3. This could not be reasonable grounds to suspect. But a judge who started with the assumption that the defendant was just as likely to have a weapon as not to have one, would conclude that the ultimate probability that he had one was over 0.9. This would certainly be equivalent to reasonable grounds to suspect possession of a weapon.

This analysis, which uses Bayes’ Theorem (something I didn’t mention so as not to put off many readers), shows how important the initial assumption is. A judge who started with the 0.5/0.5 assumption (giving Bayesian priors of 1) would think that was a fair starting point, but was it?

The judgment does not mention whether any offensive weapon was found in the defendant’s possession; other specified incriminating things were found, in respect of which he was charged.

Advertisements