Thousands of North Texas DWI convictions could be at risk after the testimony of a state forensic scientist whose work is key to such cases recently came under scrutiny.

One defense attorney has described the issue as a "big mess," and the continuation of a hearing next week could clarify the lab expert's testimony and determine whether he faces any repercussions.

In the cross hairs is Christopher Youngkin, who does blood alcohol testing for the Texas Department of Public Safety's crime lab in Garland and testifies about his findings in court. On Wednesday, he took the stand on a misdemeanor driving while intoxicated case in Collin County and ended up invoking his Fifth Amendment right not to testify.

At issue is whether Youngkin may have given conflicting testimony under oath about a 2013 lab error in which he mixed up the results of two blood samples submitted by Anna police. A report Youngkin sent to police there showed a woman who had not been drinking had a blood alcohol level of nearly twice the legal limit.

The error was discovered within days, the samples were retested and no one was harmed. The mix-up was deemed an isolated incident, according to a DPS report completed by Youngkin.

But how that error has been handled since 2013 has caught the attention of local defense attorneys. They are looking into not only whether Youngkin may have given conflicting testimony about the mistake but also whether they should have been made aware of the 2013 lab error sooner.

According to a partial transcript of Wednesday's hearing, defense attorney Troy Burleson questioned Youngkin about a Dallas County case in which he testified he switched vials in 2013. Burleson then asked about Youngkin's testimony in the Collin County case in which he stated that he had never switched vials.

"We have two inconsistent statements that cannot both be true," Burleson's law partner, Hunter Biederman, said after the hearing.

County Court at Law Judge Lance S. Baxter advised Youngkin during the hearing that he had the right to remain silent and the right to consult an attorney. When Youngkin invoked his right not to testify, the hearing came to an end. It is scheduled to resume next week.

Credibility at issue

Longtime Dallas defense attorney Barry Sorrels said the judge's warning to Youngkin, an expert witness for the prosecution, is a rare occurrence.

"That really is an attention-getter as far as what the judge's view of this witness's credibility was," said Sorrels, who is not connected with the case.

A spokesman for the Department of Public Safety on Friday declined to answer any questions about Youngkin or the issues raised by defense attorneys.

"This is an ongoing criminal trial, and it would not be appropriate for us to discuss at this point," DPS spokesman Tom Vinger said in an email. "The relevant facts will be argued in a courtroom, which is the appropriate venue for an ongoing case."

The Garland crime lab handles blood alcohol testing for seven counties: Collin, Dallas, Denton, Tarrant, Rockwall, Cooke and Grayson counties.

This car crushed in a drunken driving wreck was on display in a joint Dallas County & Tarrant County DWI Press Conference in November 2014. (File photo)

The Collin County district attorney's office also declined to comment on the pending case. District attorney's offices for Dallas and Denton counties, who also use Youngkin as a witness, say they are monitoring the situation.

"It is too early to speculate what effect, if any, Wednesday's hearing in Collin County will have on Denton County cases involving Chris Youngkin," Michael Moore, chief of Denton County's felony trial division, said by email.

A statement from Dallas County reads in part: "It is the duty of the Dallas County district attorney's office to seek justice. Each day, we work to ensure that we are using reliable and ethically obtained evidence in prosecution. ... This is an evolving situation that we will continue to monitor as we move forward in our representation of the Dallas County community."

Unaware of error

Biederman said a Dallas County jury found a client not guilty of drunken driving last month, in part, he believes, because of cross-examination of Youngkin over his 2013 lab error.

Before that case, Biederman said, his firm wasn't aware of the mistake.

"Most people haven't had the opportunity to know about this and either use it in trial, use it in pre-negotiations or use it in punishment," he said.

There's no guarantee of getting an acquittal, said Biederman. But the lawyer added that the questions raised about it could lead to conviction of a lesser offense, which means a less severe punishment.

Biederman's firm in Frisco has already identified dozens of its DWI cases involving Youngkin, but it will wait for the outcome in the Collin County case before deciding how to proceed.

"Potentially, anybody that was convicted in the past would have the right to a new trial," Biederman said.

Information released

It's unclear when Collin County prosecutors began sending notices to defense attorneys about the 2013 lab error. Biederman said his first notice from Collin County came earlier this month.

Moore said Denton County began sending the notices after prosecutors learned about the error through testimony in January. Dallas County said in its statement that its practices call for releasing any potentially exculpatory information as soon as the office is made aware of it.

Each office released a different type of information, according to Biederman. Denton County sent a transcript of the January testimony describing the error. Dallas County provided a copy of the DPS report. Collin County gave excerpts from the DPS report that summarized what happened.

Sorrels said the law doesn't require the information about potential witnesses to be released in a certain format or even that it be uniform among jurisdictions.

What is more troubling, he said, are the transcripts filed this week as part of the Collin County case.

"The inconsistent testimony about the mistake under oath in separate trials is far more important than the mistake itself," Sorrels said.

"Criminal lawyers in this state are networked, and those transcripts with inconsistent testimony will spread like wildfire. It goes directly to the heart of the credibility of this expert being called by the state."