Dr. Thomas Michael Dixon’s Love Triangle Murder-for-Hire Case

The Dr. Thomas Dixon murder-for-hire case is the 2012 killing of Lubbock pathologist Dr. Joseph Sonnier III, arranged by Amarillo plastic surgeon Dr. Thomas Michael Dixon after Sonnier began dating a woman Dixon had been involved with. Dixon paid a friend, David Shepard, in silver bars and Cuban cigars to carry out the murder. He was ultimately convicted of capital murder and is serving life in prison without the possibility of parole.¹

The Love Triangle Behind the Killing

Richelle Shetina first met Dixon in 2008 as a client at his Amarillo spa. They began an affair in 2010, and when Dixon’s wife found out, she filed for divorce the next day.² Shetina eventually ended the relationship, describing it as volatile.¹

In July 2011, Shetina met Dr. Joseph Sonnier III at a Lubbock dance studio. Sonnier, 57, was chief of pathology at Covenant Health System.³ She later called him the love of her life.⁴ In September 2011, Shetina texted Dixon that she was in love with someone else.⁵

The Murder

On the night of July 10, 2012, Sonnier was ambushed at his home in southwest Lubbock. He was shot five times and stabbed eleven times. Landscapers found his body the next day after he missed work.⁶

The killer was David Shepard, a friend and business associate of Dixon. Shepard later said he used a Gatorade bottle to muffle the gunshots and claimed the shooting was unintentional, saying he stabbed the body afterward to disguise the crime.⁷

How the Plot Unraveled

Within days, Shepard’s roommate Paul Reynolds walked into a Lubbock police station and named Shepard as the killer. Reynolds said Shepard had been confessing details while on medication and that he feared for his own safety. He gave officers information that had not been released publicly, which helped them corroborate his account.⁸

Shepard told police Dixon had paid him three silver bars and a box of Cuban cigars, and had supplied the gun.⁹ Shetina, meanwhile, pointed detectives toward Dixon, telling them she believed he had not taken their breakup well.¹⁰

The evidence trail was extensive. Phone records showed Dixon and Shepard exchanged 41 calls and texts on July 10 alone. Months earlier, Shepard had texted “Perfect day to travel to hub city,” and Dixon replied, “Need it done ASAP.” Cell-site data placed both men near Sonnier’s home on March 12, 2012, and a Plainview gas station receipt put Dixon on the route to Lubbock that day, contradicting his claim he had never been there.¹¹

Pawn shop records showed Shepard sold one silver bar in Amarillo on June 15, 2012, and two more on July 11, the day after the murder. Police divers pulled the .25-caliber murder weapon from a lake in October 2012. Dixon’s stepbrother testified he had given the pistol to Dixon in 2006, and a firearms examiner matched shell casings from the scene to it.¹² Shepard’s phone held photos of Sonnier’s backyard time-stamped the day of the murder, along with searches for spy gear, an “Assassin’s Bible,” and precious metal prices.¹³

After his police interview on July 11, Dixon deleted messages from his phone and jumped into a swimming pool with it. He had backed the messages up to a laptop, and forensic investigators recovered them anyway.¹²

Shepard’s Guilty Plea

On September 16, 2013, Shepard pleaded guilty to capital murder. Prosecutors dropped a second count and agreed not to seek the death penalty. He received life in prison without parole, waived his appeal rights, and was expected to testify against Dixon.¹⁴

The First Trial and Mistrial

Dixon’s first trial began in October 2014 in Lubbock. He was indicted on two capital murder counts, one for remuneration and one for murder during a burglary.¹⁵

Then the case cracked. Shepard, the state’s star witness, took the stand and recanted, saying he had acted alone and that Dixon had nothing to do with the killing.⁵ Prosecutors played his earlier videotaped confession, but the jury was instructed to use it only to weigh his credibility, not as substantive proof of Dixon’s guilt.¹⁶

Dixon’s defense argued he had hired Shepard only to photograph Sonnier with other women to damage the relationship with Shetina, and framed the silver bars as a business investment. Dixon took the stand and admitted lying to police about knowing Sonnier, but maintained he had only paid for surveillance.¹¹ After about eight hours, jurors deadlocked 10–2 for conviction. Two holdouts said the contrast between Shepard’s confession and his recantation left them unpersuaded that Dixon orchestrated the killing.¹⁶ The judge declared a mistrial.¹⁷

Conviction on Retrial

The retrial began in October 2015, and prosecutors changed their approach. They did not call Shepard. Instead they leaned on two witnesses who had not testified the first time.⁵

Paul Reynolds described Shepard’s confessions, the silver-bar payment, and the Gatorade-bottle silencer.⁸ Haley Shepard, David Shepard’s daughter, testified she did not believe her father’s recantation. She said that on Father’s Day 2012, her habitually broke father, behind on child support, suddenly had money for a shopping spree, a new grill, and a $200 steak dinner. When she asked where it came from, he told her, “I did some work for Mike and he paid me early,” and told her not to ask again.¹⁸

On November 18, 2015, the jury convicted Dixon on both counts of capital murder. He was sentenced to life in prison without parole.¹

The Appeals

Dixon’s team raised 50 issues on appeal, built around three arguments: insufficient evidence, admission of cell-site location data obtained without a warrant, and the trial judge’s exclusion of spectators.¹⁵

On December 13, 2018, the Seventh Court of Appeals in Amarillo reversed his conviction. The court found the trial court improperly admitted warrantless cellphone location data, citing the U.S. Supreme Court’s 2018 ruling in Carpenter v. United States, and also found the trial judge had violated Dixon’s right to a public trial by shutting out spectators once the seats were full.¹⁹ Dixon posted a $2 million bond and was released on January 28, 2019.⁵

Prosecutors took it up. On January 15, 2020, the Texas Court of Criminal Appeals unanimously reinstated the conviction. Presiding Judge Sharon Keller wrote that any error in admitting the cell-site data was “clearly harmless” beyond a reasonable doubt, given the other evidence of Dixon’s movements and lies, and found no preserved error on the public-trial claim. The case went back to the Seventh Court to address 37 remaining issues.²⁰

On January 13, 2022, the Seventh Court affirmed the capital-murder-for-remuneration conviction but reversed and acquitted Dixon on the second count, holding that convicting him twice for the same victim’s murder violated the Fifth Amendment’s double jeopardy protection.¹⁵ Because capital murder carries a mandatory life-without-parole sentence in Texas, dropping the second count did not change how long he serves.²¹

Where the Case Stands Now

In April 2024, Dixon filed a writ of habeas corpus in state district court in Lubbock, raising 47 grounds for relief. His claims include ineffective assistance of counsel, allegations that detectives used false evidence involving discrepancies between Central Standard Time and Central Daylight Time in police reports, and denial of due process. That petition is pending, and Dixon remains in the custody of the Texas Department of Criminal Justice.²²

On the civil side, Sonnier’s sons, Joseph “Dallas” Sonnier IV and James Sonnier, filed a wrongful-death lawsuit against Dixon and Shepard seeking at least $1 million. Judge John Grace set the case for trial in 2025.²³ On August 18, 2025, days before trial, the family withdrew the suit. Judge Grace granted the nonsuit with prejudice, barring them from refiling. Court documents did not say whether the parties settled or the family simply dropped the case. The judge ordered the Sonniers to bear the legal costs, a ruling described as common in voluntary dismissals and not necessarily an indication that no settlement was reached. Attorneys on both sides declined to comment.²⁴

1
ABC News. Texas Doctors Love Triangle Timeline of Events
2
NewsChannel 10. Day Thirteen Thomas Dixon Murder Trial
3
KCBD. Covenant Chief Pathologist Victim of Apparent Homicide
4
Good Morning America. What Happened to Texas Doctor Killed in Alleged Murder-for-Hire Plot
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ABC News. What Happened to Texas Doctor Killed in Alleged Murder-for-Hire Plot
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EverythingLubbock. Love Triangle Ends With Murder-for-Hire in Lubbock
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ABC News. Hitman Involved in Texas Doctor’s Murder-for-Hire Love Triangle
8
NewsChannel 10. Thomas Michael Dixon Re-trial Day 4
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NewsChannel 10. David Shepard Pleads Guilty to Sonnier Murder
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Amarillo Globe-News. Girlfriend in Sonnier Case Breaks Her Silence
11
FindLaw. Thomas Dixon v. The State of Texas
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FindLaw. Thomas Dixon v. The State of Texas (7th Court of Appeals)
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Lubbock Avalanche-Journal. Messages Between Dixon and Shepard Focus of Day 8 of Dixon Murder Trial
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CBS News. Texas Man Gets Life in Prison for Killing Doctor in Murder-for-Hire Plot
15
KCBD. Dixon Still in Prison for Capital Murder After Amarillo Court Dismisses Second Count
16
ABC News. Jurors in Texas Doctor’s Love Triangle Murder-for-Hire
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Lubbock Avalanche-Journal. Mistrial Declared in Dixon Murder-for-Hire Trial
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Lubbock Avalanche-Journal. Eldest Shepard Daughter Tells Jurors Father Was Dishonest
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Amarillo Globe-News. Lubbock DA Seeks $2 Million Bond
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Texas District & County Attorneys Association. Takeaways From Dixon v. State
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NewsChannel 10. Former Amarillo Doctor to Stay in Prison After Court Affirms Murder-for-Hire Conviction
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EverythingLubbock. Love Triangle Ends With Murder-for-Hire in Lubbock, Convicted Doctor Makes New Filing
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Lubbock Lights. Dr. Sonnier’s Sons’ Long-Delayed Civil Lawsuit Seeks at Least $1 Million
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EverythingLubbock. Murder-for-Hire Love Triangle Lawsuit Shuts Down