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ST. LOUIS COUNTY, Mo. – An unusual defense has arisen in a high-profile murder trial in St. Louis County. Beau Rothwell is accused of killing Jennifer Rothwell in November 2019. Rothwell, who was pregnant at the time, was 28.

Beau Rothwell’s lawyer does not dispute that Rothwell struck a fatal blow to his wife’s head, but the defense claims Beau did not plan to commit murder. Attorney Charles Barberio says it happened after an argument in which Beau told Jennifer that he’d been having an affair.

This story first hit the news during a November 2019 snowstorm. Beau reported his wife missing on November 12. Creve Coeur police later found Jennifer’s car abandoned on the side of Olive near Fee Fee, which is a very busy intersection. It was about a mile from the Rothwells’ home, which was in an unincorporated part of St. Louis County.

While Rothwell pretended to search for his wife, St. Louis County detectives found evidence of blood clean up. Search warrants also revealed Jennifer had recently Googled the topic, “what to do if your husband is upset you are pregnant.”

Jennifer’s body was discovered along a heavily-wooded area of Highway 61 in Lincoln County.

Beau’s defense team said the pregnancy was not a surprise to the defendant and that Rothwell was happy about it. The problem, the defense said, arose from a sexual affair Beau was having that he felt guilty about and that he revealed to his wife on November 11. The two got into a fight and the defense claims Beau hit Jennifer in the heat of passion, striking her so hard that her brain hemorrhaged.

On Tuesday afternoon, Assistant St. Louis County Prosecutor Tom Smith dropped a bombshell in court by revealing Beau Rothwell’s list of pros and cons about his mistress. Rothwell wrote it on a work notebook, Smith said, dated five months before Jennifer’s murder. Beau listed “better sex life,” “more respect,” and “fresh start” in the pros column, as well as “Is the cost too high?” Under cons, indicated by a minus sign, Beau wrote, “half my assets/money,” “trust is shaken/tainted,” “my family disappointment,” and “take on her kid with his probs.”

During cross examination, Rothwell’s defense attorney, pointed out Beau’s list did not mention killing anyone.

The defense says the only planning involved was Beau cleaning up the scene and that the jury should consider that separately. FOX 2 also learned that Beau Rothwell himself may take the stand as his murder trial continues.