Attorneys for Eric Williams, accused of killing two Kaufman County district attorneys and one of their wives, begins Dec. 1, challenged the credibility of the prosecution's ballistics expert Friday.
Williams' attorney argued that the science behind proving a bullet came from a specific gun is not exact enough to be considered an expert opinion.
The ballistcs expert, who works for the Department of Public Safety, said he compared the marks on bullets fired from several guns used in crimes. Dallas Police Department ballistics expert James Jeffress said the science is more than exact enough.
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"I believe our consecutive manufactured studies, which we've been doing over 30 years, have consistently demonstrated that we can do what we say we can do," he said. "The barrel test has been taken by 508 examiners in 20 different countries, with an error rate of less than 1 percent."
Former Justice of the Peace Eric Williams is charged with murder in the deaths of Mark Hassee outside the Kaufman Courthouse and Mike McClelland and his wife in their home in 2013.
Williams' trial begins Dec. 1.