Drug trials often see the Crown tender telephone intercepts of coded conversations between an accused and their associates to support a submission that the interlocutors were talking about drugs; or at least using language consistent with talk of drugs.
It is a trite subterfuge device within the criminal community to use slang, or ‘argot’, in an attempt to render ambiguous the true meaning and effect of their conversations. Nevertheless, when evidence of such conversations is put before a jury an expert’s guidance is necessary; even though many of the coded terms would be quite familiar to any juror who has taken the time to enjoy a few episodes of The Wire in their time.
Therefore, a police officer who has spent considerable amounts of their service dealing with the criminal drug milieu and is thereby purportedly qualified to give evidence of how such people talk, will be called to give evidence.
However, there are considerable dangers in putting such evidence before a jury. The case law illustrates some of the specific forensic dangers, but there are broader perhaps intrinsic issues with a police man or woman giving such evidence which would perhaps warrant an expert being drawn from outside the police force.
A good example of problems that can arise is Keller’s case. In Keller v R  NSWCCA 204, the accused was charged with the supply of cocaine in a commercial quantity. A conviction was recorded at first instance and an appeal instituted raising an issue with regard to the opinion evidence given by a police officer as to the meanings of various words spoken during intercepted telephone conversations. Some of the more colourful language used included: ‘teeth’ (a reference to cocaine); ‘untickled’ (to purity); and ‘a farmer’ (to quantity, being a quarter of a kilogram).
At the time he gave his evidence, the expert was a member of the Australian Federal Police with extensive training and experience in drug related matters. For his opinion to be admissible under the Evidence Act (section 79) it would need to be wholly or substantially based on his training, study or experience. Yet a passage of cross-examination by the defendant’s counsel extracted by the Court of Appeal at  revealed that the opinion was not so founded:
“Q- You’ve said that the reference at page one…saying ‘that’s when I get the results’ is in your opinion a reference to a drug transaction?
Q- You can’t say that simply by reading that, someone saying he’s going to meet someone at 9 o’clock in the morning that that relates to drugs can you?
A-I placed this telephone conversation in the total context of which it was involved.
Q-What was the total context Mr Smith that’ you’re talking about, what are the contextual matters that you rely on in reaching that conclusion?
A-The fact that Mr Denholm was arrested with half a kilo of cocaine the following day.”
The central problem was the admission by the expert that “..in part the opinion of the witness was arrived at having regard to the discovery of the cocaine in the possession of the co-accused who had conversed with the appellant.” (at ); as opposed to an objective assessment based on the expert’s experience in other matters of what the words referred to.
If it wasn’t for the skilled cross-examination at trial stage and the highly skilled appellate advocacy of Stephen Odgers SC this problem would not have been brought to light.
There was also an issue with respect to the manner in which the expert’s evidence was given. He gave evidence to the effect that in his opinion the parties to the intercepted conversations were actually talking about drugs rather than using language consistent with that state of affairs. This kind of evidence had previously been ruled inadmissible in other cases on the basis that it strayed far too close to the ultimate or central issue in the trial (ie. was the accused guilty). The common law rule against evidence being given which strays too close to the ultimate issue has now been abolished by section 80 of the Evidence Act, but judges are still reluctant to allow evidence of this kind and often find other ways to reject it (eg. s135 of the Evidence Act).
On how many other occasions has a police expert given evidence of what the accused or their associates were using was drug ‘argot’ and did so with a knowledge of the facts and circumstances in which the crime took place?
I suppose as a matter of good defence advocacy, how the witness reached their opinion, including their background knowledge of the case against the accused, should be put to the expert to ensure that any of that information has not coloured their opinion, albeit inadvertently.
Nevertheless, it was somewhat fortunate for the accused that his counsel was able to point to such a particular matter as he did in Keller’s case. Even if the expert did admit to having an expensive knowledge of the facts in the case, it would be an easy submission for the Crown prosecutor to make that this level of background understanding is necessary to enable the expert to properly opine.
However, the problem remains: if you know someone is accused of a drug offence and just how the case is put against them, it is a rare individual indeed who can compartmentalise their thinking to the extent necessary to prevent the same problem as that which occurred in Keller. This is not to say that there is any lack of propriety in the way these police witnesses conduct themselves, it is simply a matter of one’s independence of thought being coloured by among other things, a combination of what we know, our experience and life’s purpose .
This is a matter a judge alone could account for by the weight they accord the evidence, but this level of skill in assessing an expert witness’ credit may well be beyond a lay juror.