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What is an expert witness?
In court, an
expert witness can provide evidence on areas beyond the
normal experience of a jury. He or she is under a duty
to be impartial, and to base his expert opinion on verifiable
fact. The standards of credibility required for expert
defence witnesses are often much higher than for prosecution
'experts'. In drugs cases in the criminal courts, Police
Officers normally provide 'expert' evidence as to the
value of drugs and how much is compatible with personal
use. They base this information on their 'experience',
which can be as little as 6 months, or gained over several
street values of drugs, some police officers give the
highest possible value of the smallest possible unit,
a basis described as similar to 'Strawberries at Wimbledon'.
These values are ostensibly based on information from
informants, defendants in custody and occasionally on
'controlled buys' by undercover officers. However, officers
may not believe prices quoted by defendants which are
lower than the accepted norm. In seizing 'proceeds of
drug trafficking' the courts will presume that a defendant
convicted of a 'trafficking offence' will have already
received as profit the 'street' value of any drugs seized.
In cases of
cannabis cultivation, people growing more than a handful
of plants are likely to face a charge of intent to supply,
and custodial sentences are commonly handed out for people
'growing their own'. Potential yields are commonly determined
from sample plants, which are not always representative
of the crop. Although forensic evidence in this area is
improving in quality, yields are commonly expressed as
including leaf, as well as bud.
consumption or intent to supply
commonly regard any quantity representing more than 1-2
days supply, and sometimes less than this, as indicating
an intent to supply. They commonly base their consumption
figures on mere guesswork. Previous surveys in this series
since 1984 have allowed a variety of defence experts in
drugs cases to quote authoritative figures on consumption
and drugs prices, and many wrongful convictions have been
avoided, or acceptable pleas negotiated, as a result.
Some prosecution witnesses have used previous survey results
in commenting on consumption of drugs.