A recent count case in Minnesota poses an interesting question. In summary, a man accused of impaired driving says he should be able to review the source code of the breathalyzer used to gather the evidence against him.

On the surface, the man’s request seems reasonable. As I understand it, the primary evidence against him is that he exhaled into a box and it displayed a number. And that number was too big.  In fact, everyone who drives, impaired or not, presumably has an interest in the accuracy of the device.

But the manufacturer, CMI, Inc., and the State of Minnesota apparently disagree, and they have convinced both the trial and appeal judges that handing over the source code would be “unreasonably burdensome.” So unless the defendant launches another appeal — or perhaps buys one and sends it to a lab for analysis — he appears to be out of luck.

I’m inclined to believe that the accused is simply looking for any possible way to have the evidence against him excluded. But that’s the way the system works. To be convicted, the accused must be proven guilty beyond a reasonable doubt. He has the right to cross examine human witnesses, so it simply doesn’t make sense that he’s not allowed to examine the functioning of the machine that says he was over the legal limit.

What could go wrong

There are a number of things that could go wrong with an electronic breathalyzer.  Presumably, aging or failing components that change the readings would be picked up during calibrations, so there are likely some procedural safeguards. But what if the developer made a mistake or took shortcuts?  Converting the output of an optical sensor into alcohol in the breath into blood alcohol levels must involve some math. What if there is a bug in the math libraries that hasn’t been discovered?

Then there are issues such as version control. Did the right software get loaded onto the device? Has it been upgraded? Can the vendor reproduce the exact code loaded onto devices sold several years ago? Has it been modified?

The last question should send shivers down a Judge’s spine. The device is in the custody of the same person who laid the charges and, therefore, has an interest in seeing a conviction. While the vast majority of police officers play by the rules, we are obliged to ask the question: What checks and balances are in place to stop that one bad apple from tampering with the device? Without appropriate safeguards, you too could be just one firmware mod away from a criminal conviction.

What should be done

An objective third party can examine all aspects of the software development life cycle, the software, the hardware, field maintenance and related security controls. If the manufacturer has done its job, the third party report will depict a reliable and trustworthy device. In fact, if the manufacturer has done its job, it should welcome the notion of an objective third party doing just that. On the other hand, if the manufacturer hasn’t done its job, we’ll all know that, as well.

According to Bill Collins, sales manager at CMI, the product was thoroughly tested by the National Highway Traffic Safety Administration, part of the United States Department of Transportation, prior to sale to law enforcement agencies. Individual States also test the device and it has been subject to other third party examinations prior to being generally accepted by the courts.  He made another very good point: Source code is only one part of the device and, to draw a meaningful conclusion, one would have to examine the entire device including both hardware and softwar.

Preserving defendant rights

While I sympathize with the company and understand its desire to keep the proprietary source code confidential, impaired driving is a crime and a conviction can have major implications, including restrictions on employment and travel. Criminal defendants must be allowed to examine the evidence against them. Intellectual property concerns are a red herring – courts have long had procedures in place to allow the examination of sensitive information in a controlled manner.

If a defendant wants to retain an expert to conduct such an analysis, he or she must be allowed to do so. If the product is solid, defendants will quickly find out that they are simply throwing their money away. Some American states including Florida agree and have upheld the defendant’s right to examine the code.

In the words of English jurist William Blackstone, “Better that ten guilty persons escape than that one innocent suffer.”  Allowing any black box to produce evidence is a slippery slope that we can’t afford, and product vendors should take note. It won’t be long until other devices like digital recorders are subject to the same scrutiny. Until we illuminate inside, outside and around the box there is no justice.

One Response to Evidence from a Black Box

  1. Brenda Hollingsworth
    Feb 14, 2009

    Very insightful article that articulates fairly the right of an accused person to test the evidence against him or her. We’d like to link it to our criminal law blog.

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