Prosecutors in pot-legal Colorado are expressing frustrations that they are having a tough time finding juries willing to convict some suspects who have been charged with driving under the influence of marijuana.

According to CBS Denver, Colorado District Attorneys’ Council head Tom Raynes said that juries are in some cases refusing to convict individuals who have been found driving with levels of pot in their system exceeding the 5 ng/ml THC legal limit.

“You are putting lives in danger. I want the message to be understood. It’s about driving while under the influence of drugs — it’s not about recreational or medical, it’s about being impaired when you drive,” he said. “I don’t believe anyone can drive better under the influence of any substance.”

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CBS Denver pointed to the case of medical marijuana patient Melanie Brinegar as an example. Brinegar was charged with driving under the influence of pot during a June traffic stop over an expired license plate. Though she admitted to having used marijuana and was found over the legal limit, officers did not witness her driving erratically.

Brinegar claimed that marijuana use improves her ability to drive and that she was neither high nor impaired. She was acquitted by a jury of her peers.

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The Free Thought Project characterized the jury’s refusal to convict as “jury nullification.” However, it appears that a component of the law allows juries to find defendants not guilty even if they are above the legal limit.

Brad Wood, a foreman on the jury that acquitted Brinegar, said, “The law allows you to infer that the person was impaired if they have over 5 ng/ml. But you may also feel free not to infer that and in any case use all the evidence to make your judgement… If the law says we strongly encourage you to weigh this as the biggest factor, I think it would have been a whole different story… If the officer said, ‘We saw her weave,’ it probably would have been a different story.”

Wood referred to the law as poorly written and said that the jury believed Brinegar’s claim that marijuana does not impair her driving.

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During the trial, Brinegar’s attorney Colin McCallin argued that the pot driving impairment law differs from driving under the influence of alcohol laws that require juries to convict simply on the basis of the suspect’s blood alcohol content. McCallin said that this argument might not work in other incidences in which an individual has been charged with driving under the influence of marijuana.

“Are we sending a message it’s okay to smoke and drive? I don’t like that message. In [Brinegar’s] case maybe its fine,” Wood said.