The issue in this aspect of the case is whether a defense expert collected evidence from the crime scene and then withheld it from the prosecutors. Sara Caplan was part of Phil Spector's original defense team (since replaced) which went to the music producer's mansion. She reportedly saw forensic expert Henry Lee pick up a small object that might have been a piece of the dead woman's acrylic fingernail and put it in a vial. Mr. Lee denies doing so.
When Ms. Caplan initially refused to testify citing lawyer-client privelige, she was held in contempt of court and the California Supreme Court refused to hear the appeal of the contempt charge. She has now agreed to testify.
When it comes to withholding or tampering with evidence, the assumption most people make is that defense attorneys and their staff and/or experts either never do this or that it is legal and ethical for them to do so and therefore it should never be an issue during the trial.
In my opinion tampering is tampering.