For part two of “Blood Will Tell,” her New York Times Magazine/ProPublica investigation into Joe Bryan’s murder conviction and the use of blood spatter analysis as a forensic tool, Pamela Colloff took the same 40-hour course that is the sum total of the training many blood spatter experts can claim. It did not inspire confidence in the precision or reliability of the experts’ testimony.

On the last day of class, I was given my “certificate of training” after receiving a 97 on my final exam. Everyone in my class passed. Griffin had told us that even if we failed the final, we would still receive a certificate of completion, but rarely, he added, did anyone fail. Our scores on our final exams were not recorded, he assured us, nor were the exams preserved. “Don’t worry that an attorney is going to come back and say, ‘You missed Question 14,’ ” he explained.

From time to time that week, Griffin cautioned us: “You won’t be walking out of here an expert. You’ll know just enough to be dangerous.” It was a startling statement, because judges across the nation have allowed police officers with no more training than we received — 40 hours — to testify as experts. Griffin reminded us that our class was merely an introduction to bloodstain-pattern analysis, and that we would need to complete an advanced class and a mentorship program before we would be proficient enough to call ourselves experts. Yet he advised us on what to say if we were called to testify in court. On the stand, he suggested, we should avoid saying what “probably” happened, because that would give an attorney who cross-examined us an opening. “You’ll be asked: ‘How probable? Eighty-five percent? Seventy-five percent?’ And you can’t say,” he told us, alluding to the fact that an analyst’s theory of a crime often cannot be substantiated with hard numbers. It was less risky, he said, to state, “The best explanation is…”

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