Mark Ryan Thiessen

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Mark Thiessen is a criminal trial lawyer and the Chairman/CEO of the Thiessen Law Firm in Houston, Texas. Mark earned the American Chemical Society-Chemistry and the Law (ACS-CHAL) Forensic Lawyer-Scientist designation, which is the highest form of scientific recognition available for lawyers. Mark is a frequent legal seminar lecturer, author of numerous published legal articles, and a LawLine and HBA faculty member. Mark is the current DWI Committee chair for Texas Criminal Defense Lawyers Association (TCDLA), on the Board of Directors for Harris County Criminal Lawyers Association (HCCLA), and a Charter Member and Director for DUI Defense Lawyers Association (DUIDLA). Mark is a Texas Super Lawyer and was awarded the 2012 Unsung Hero Award by HCCLA.

Stories from Mark Ryan Thiessen

Back to Basics: Attack SFSTs, Not the Officer
Friday, February 14th, 2020

In the heat of trial, all trial attorneys fight vigorously for their DWI clients. In that fight, it’s understandable that you want to destroy the officer, destroy the Standard Field Sobriety Tests (SFSTs), and vindicate your client.

2019’s Need-to-Know Changes to DWI Law
Friday, November 8th, 2019


Together, House Bills 20482 and 35823 refashioned Texas DWI law and punishment—and finally abolished surcharges. Kind of.

Not Guilty v. Cerberus: Winning Intoxicated Manslaughter Trials
Friday, March 9th, 2018

“Ma’am, we regret to inform you, but your son was killed by a drunk driver.”

“Ma’am, we regret to inform you, but your son has been arrested for killing someone while driving intoxicated.”

Candida albicans, the Yeast Syndrome, and the Auto-Brewery Syndrome
Tuesday, May 9th, 2017

Whether blood samples used in forensic science Driving While Intoxicated (DWI) testing can be affected by endogenous ethanol production is a recurrent and yet unresolved defense. The basis of endogenous ethanol production is whether microbial growth can occur to falsely elevate the ethanol concentration in forensic blood samples.

Fear and Loathing in South Texas
Saturday, November 21st, 2015

The sweet acrid smell of a freshly lit cigarette danced inside his nostrils, seeping into his unconscious brain, waking him. His eyelids twitched and tremored, but did not open. It was an auto somatic response; like a mother drawn to her crying babe. Not something sought out. It was more a keening allure; an impulse impossible to ignore. Vices. Lovely reliable vices.

Intoxilyzer™ 9000 in Texas
Thursday, August 13th, 2015

However, Texas is currently transitioning to the Intoxilyzer 9000 and training breath test operators through local technical supervisors. Implementation of the Intoxilyzer 9000 was scheduled for Summer 2015, but due to software issues and bugs, the 9000 has not been approved for evidential use.

Not Guilty v. Goliath: Conquering Giant Blood Tests Using the Disconnect Defense
Saturday, December 6th, 2014

Finally the day has come: Written on the face of the State’s file, in big red letters, is the blood test result. Most attorneys cringe when the lab result reveals a blood alcohol concentration over a 0.15.

Eleven Essential DWI Trial Tactics
Wednesday, June 4th, 2014

"We, the Jury, find the defendant not guilty.” Makes your hair stand on end, drops the weight from your shoulders, and weakens your knees. No sweeter words are ever heard by criminal defense attorneys standing shoulder to shoulder with their clients.

Drawing the Blood Test From a DWI Case
Tuesday, October 1st, 2013

The era of the total-refusal DWI case is quickly coming to a close in Texas. Gone are the days of refusing a breath test without concern for something more invasive. DWI blood test trials are the future for the criminal trial attorney.

Storytelling Closing Arguments
Thursday, September 6th, 2012

“May it please the court, opposing counsel…Ladies and Gentlemen, thank you for listening to all the evidence. . . .” Just about this time, juries’ eyes glaze over; they shift focus and start daydreaming. You have just lost the jury.