I think Bullcoming has the right argument:

A lab analyst who comes to court to testify about the numbers generated by a machine, Bullcoming’s lawyers argued, is like an eyewitness who claims to have seen a license-plate number: the observations of each should be subjected to testing in court, in front of the accused.

The defense has a right to question the analyst about his qualifications, his methodology, chain of custody of the sample, and other aspects surrounding his testing. The analyst who performed the test in this case is on unpaid leave. The surrogate witness wasn't with him when he performed the test. He's just familiarized himself with the results. What if the analyst was drunk when he made the test? What if he didn't perform it properly? What if he grabbed the wrong sample? There are many questions that could effect the reliability of the report or the witness that can only be answered by the person who conducted the tests.

Who to watch at oral argument? Justice Scalia, who as we learned from his dissent Monday in Michigan v. Bryant, is a passionate defender of the Confrontation clause.

Too many defense lawyers stipulate to the identification of a drug. It's an element to be proved just like any other. At a federal cocaine trial in the 70's, where my client was charged with selling 4 kilos of coke, the DEA chemist had flown in from San Francisco to testify. She said on the stand, during cross-examination by my co-counsel, that she had changed her notes on the plane. Train wreck for the Government, which immediately offered our client a misdemeanor.

Given the increasing instances of lab fraud and incompetence contributing to wrongful convictions, allowing a surrogate witness to testify in lieu of the person who performed the test is a terrible idea.

The Sixth Amendment guarantees a defendant the right to cross examine the witnesses against him. When a witness testifies to a conclusion, that a certain sample contains x amount of a specific substance, that's testimony and evidence that goes to the heart of an element of the charged crime.

Here's the amicus brief of the National Association of Criminal Defense Lawyers, which posits (correctly in my view:

Gas chromatography testing for blood alcohol involves the exercise of judgment and presents a risk of error by the analyst that can be discovered only through cross-examination of the actual analyst who ran the test.

The brief points out:

As this Court recognized in Melendez-Diaz, confrontation is the best instrument to uncover ignorance, incompetence, mistake, or even fraud in the context of forensic science. 129 S. Ct. at 2536. Despite the aura of reliability that science lends them, forensic laboratory reports are as prone to error and fraud as the ex parte affidavits the Confrontation Clause was designed to prohibit. “Forensic evidence is not uniquely immune from the risk of manipulation.” Melendez-Diaz, 129 S. Ct. at 2536.

....Accurate and valid results depend upon the knowledge of the analyst to perform the protocol correctly, the integrity of the analyst to not improperly modify the results in one way or another, and the prior calibration with ethanol standards of known concentration being completed properly. The critical steps upon which the ultimate accuracy relies occur early in the preparation of the sample for analysis. Mistakes made by the analyst are not necessarily discernable to anyone else.

The surrogate witness is not an acceptable substitute:

Cross-examining a surrogate witness is like cross-examining a textbook – an attorney can only discover what should have happened rather than what actually happened. This does not assist the factfinder or the search for the truth. If the actual analyst who performed the blood alcohol analysis strayed from the accepted procedure for conducting the test, or routinely disregards certain protocols, the defendant cannot discover this from cross-examining the surrogate.

We need the Court to stay on the path it chose with Melendez-Diaz and Crawford. No retreat, no surrender. I hope Justice Scalia doesn't let us down -- and that his powers of persuasion with his fellow justices are greater than they were Monday in the Michigan case.

The Innocence Project's Amicus brief is here.