Let me tell you about one of our DUI cases that ended up on the front pages of the Los Angeles Times. My law firm had a young client, I’ll call him "Steve", who had been arrested for drunk driving by the Los Angeles Police Department and a blood sample drawn from his arm. He swore to us that he was innocent, and after interviewing witnesses and reviewing the evidence we believed him.
Problem: the blood alcohol content of the sample was .15% — almost twice the drunk driving limit.
We obtained a portion of the sample from the LAPD crime lab and sent it to a private lab that we use for reanalyzing blood of all our DUI clients. The lab reported the blood alcohol level to be .13% — lower, but a long way from being under .08%. As we requested, they also tested for preservative and anticoagulent (either fermentation or coagulation can raise the alcohol level in the sample), but everything was in order. Steve still insisted he was not driving under the influence of alcohol.
The only other possibility was a faulty "chain of custody". In other words, LAPD lab got the vial mixed up and tested someone else’s blood. Kind of like the work they did in the O.J. Simpson case. So we had the sample blood-typed to see if it was that of another arrestee. Result: type "O"– the same as Steve’s. But, then, that’s the most common type of blood.
We decided to try something different, something that, to our knowledge, had not been done before in any DUI case. We had blood taken from our client and, along with a portion of the remaining sample from the LAPD lab, shipped to a laboratory that specialized in DNA testing. A month or so later the report came in.
The blood tested by LAPD was conclusively not Steve’s.
The prosecutor in the case initially refused to accept these results. But after we proved that the comparison blood had come from our client and after LAPD checked the blood themselves, he reluctantly dismissed all criminal charges. Predictably, according to the L.A, Times, LAPD tried to point the finger at someone else: "Police officials said they are investigating how the mix-up occurred and who is responsible, But, they said, they are fairly confidant that the lab did not make a mistake." One possible explanation, they said, was that the blood was mistakenly labeled when it was initially drawn by nurses at LAPD’s jail intake facility in Van Nuys.
So how could this have happened? The truth is that it probably happens far more commonly that we suppose.
When a blood sample is drawn from the suspect in a DUI case rather than using a breath machine, the sample is supposed to be inserted into a vial containing preservative and anticoagulent, then sealed. Procedures then require that a chain of custody be established: the location of the vial of blood must be identifiable at all times so that it does not become contaminated or mixed up with someone else’s vial. This is done by labelling the seal with identifying information, then usually placing the sealed vial in an evidence locker (which should be refrigerated but often is not) until it is transported to the crime laboratory for further storage.
At any stage of this chain of custody, of course, things can go wrong with the vial or the records. It may be a week or so before the vial is finally analyzed. This is usually done using gas chromatograph instruments, and the vial is one of many analyzed in large "batches". A batch is a group of blood vials, perhaps 40 or more of them, which are analyzed in sequence; this is much faster and more economical than isolating, identifying and separately analyzing one vial afer another.
Of course, it is critically important that the sequence of tests by the gas chromatograph coincide with the sequence of vials in the records. If the sequence of numbering of the vials is off by one, then the records will show a result from the analysis of another vial. And it won’t be just one person whose blood is falsely reported: every vial may also be off — and will all be wrong. And you have 40 people people facing criminal charges based upon false evidence.
"How do I know the blood they tested was mine?" Simple — if you can hire a top DUI attorney, get a portion of the sample from the crime lab, and then have an extra $1500 laying around for DNA testing. Otherwise, I guess you’ll never know….