Let's get the legal issue out of the way first, then I can tie some science into this.
The US Supreme Court took a case this week regarding the right of a defendent to question the scientist/techniciam who prepared a scientific report used by the prosecution.
You can read the summary of the case and the oral arguments online.
The US Constitution guarentees the right to confront one's accuser's, but certain documents have been found over time to be exempt from this - such as ordinary business records, accounting books,... The question here is whether the lab report is such a record.
I certainly do not think that it is one for a number of reasons, some of which were raised: lab tests are not 100% reliable, the standard procedure(s) may not have been followed... All true, but I think they missed a crucial distinction.
Despite the reputation, science is very much a human effort frought with errors. The scientific method which everyone is taught is "hypothesis --> experiment --> data --> resuts --> conclusion(s), but no one is ever taught that the last link is the weakest. Drawing a conclusion is where a human being enters the picture.
As such, the lab reports at issue in this case are not just a business record, but actually have a conclusion in them and that conlusion is subject to error. Accounting books do not have a conclusion in them - both side are free to argue whatever they desire of them. That is the distinction, and this basis was dissappointingly not used in the oral arguements.