OK, so, this one was REALLY long…I’m sorry, but I never promised brevity here.
On December 19 or 20, 2020, 4-year old Jessica Mast was murdered by being beaten, dunked in a lake in near-freezing temperatures, and then left outside for an unknown period of time. (Although her date of death is typically listed as December 20, the beating that led to her death began on December 19; she had also been regularly beaten in the preceding weeks.)
Within a few days, four people had been arrested and charged as co-defendants in her murder: Ethan Mast (Dec 21, 2020), Kourtney Aumen (Dec 21, 2020), her father James Mast (Dec 24, 2020), and her mother Mary Mast (Dec 24, 2020). Although the exact charges changed as the case developed, the charges as the four approached their trial dates were first-degree murder, abuse of a child, child endangerment, assault, and armed criminal action.
On Feb 24, 2022, Ethan Mast pled guilty to second-degree murder and first-degree or attempted assault involving serious physical injury or a special victim. On Jan 24, 2023, Mary Mast pled guilty to first-degree child endangerment, for the abuse of her 2-year old son). (Although this is speculative, it is possible that Mary Mast’s final charge is less than the others because she was also hospitalized due to the abuse she received from Ethan Mast and Kourtney Aumen.) On Nov 25, 2024, James Mast pled guilty to second-degree murder and first-degree or attempted assault involving serious physical injury or a special victim.
Almost 6 years after the murder of Jessica Mast, on Oct 6, 2026, Kourtney Mast pled guilty to second-degree murder and first-degree or attempted assault involving serious physical injury or a special victim. With Kourtney Mast’s guilty plea, the full trial process for all four co-defendants is now almost officially complete; none of the four could be sentenced until the guilt phase was complete for all four, so that is what remains. Kourtney Aumen’s sentencing is currently scheduled for Dec 21, 2026, six years to the day she was initially arrested.
Originally my understanding of this case was centered around the change of venue for Kourtney Aumen and questions about her competency. But, when I was talking to someone about the case, I heard about a social media post that wondered how Kourtney Aumen grew into a person who would do these things and the lack of accountability for violence in Anabaptist communities. Good point…which apparently set off a flurry of support Kourtney Aumen as a victim herself. This just didn’t match my memory of the case, which was Kourtney Aumen actively abusing Jessica Mast, her 2-year-old brother, and her mother, Mary Mast, so I wound up going down the rabbit hole of motions and findings available as part of public record at the Missouri Courts website (https://www.courts.mo.gov) for the Kourtney Aumen case, and they are absolutely wild.
Although Kourtney Aumen only has 4 cases listed, each case has several aspects, so there is a history of motions and findings over the past (almost) 6 years, including a motion to change the venue from Benton County, Missouri, which was sustained. The trial would have been held in Webster County, Missouri. However, as the judge presiding over the case still came from Benton County, many of the pretrial motions were still addressed in Benton County. Change of venue motions are often denied, so the fact that Kourtney Aumen’s venue change was sustained is unusual.
There is even an order to put the case at Security Level 3 once jury summonses are sent and until selection is complete so that potential jurors cannot use Case.Net to discover information about the case, thereby prejudicing this jury in this new venue. This is completely valid (where did I get my information, after all?), and speaks to why the change of venue was so necessary. Of course, with a guilty plea and the cancellation of the jury trial, that will not be necessary now.
However, the largest focus over the past 6 years has been Kourtney Aumen’s competency, as she has cycled between being found competent and incompentent. The discrepancy seems to hinge on whether or not someone with Intellectual Disability – Mild (her most common diagnosis) could understand the proceedings and assist in their defense. It’s worth noting that, according to the APA, people with the “mild” level of intellectual disability have intellectual deficits (IQ scores that typically range between 50 and 69), deficits in one area of adaptive functioning (social, practical, or conceptual), and these deficits being present since childhood. IQ scores are not enough for that diagnosis; there must be one (and only one, if it is mild) adaptive functioning deficit as well. Many people with Intellectual Disability – Mild, with support as children and continuing supports, can live independent lives.
This is a far cry, by the way, from someone with a profound level (the most severe level) of intellectual disability. Children who are identified at an early age can get the supports they need and build independence as they age. However, they do often need routine, as new expectations strain the adaptive skills they have developed. As a result, it is possible someone found competent to stand trial at one point could be considered incompetent at another; at that point, they would need competency restored, but that is entirely possible. And this is where things go off the rails.
One sign of what may have been to come was through a motion from the defense to strike a prosecution witness, Dr. Rosario, who “claims specialized training in ‘coercive control, undue influence, and cult and high-control group dynamics, including training in coercive control and influence dynamics and coercive control’” (https://www.courts.mo.gov/fv/c/Motion%20to%20Strike%20Testimony%20and%20Report%20Submitted%20by%20Felicia%20Rosario,%20M.D..PDF?courtCode=30&di=4159390). They follow that with stating she has argued that “Opinion 1: Aumen’s documented intellectual limitations do not, on their own, determine her capacity to exercise interpersonal influence over other adults, and Opinion 2: The group’s existing religious beliefs provided a framework through which Aumen could acquire and exercise influence.” and that they find it laughable someone with an intellectual disability would be able to influence others who are smarter than she is, and surely that is not what Dr. Rosario is proposing. (Spoiler alert: yes, that is entirely possible, because some pretty smart people find themselves being influenced all the time.) They are correct this is not about competency per se, so Dr. Rosario’s testimony would not be directly relevant to Kourtney Aumen’s competency, but the idea that she could influence others is not laughable at all.
However, in the flurry of motions and findings, especially over the last 5 months, including two that I can only professionally describe as serious scoldings, it becomes clear that Kourtney Aumen understands the case against her, can accurately separate the consequences of different charges, and reason about them.
For whatever reason, two defense experts were totally problematic. One of those experts is Dr. Rose, who appears to have assessed her for a potential not guilty by reason of insanity (NGRI) plea and argued she could not understand the wrongfulness of her actions (https://www.courts.mo.gov/fv/c/JUDGMENT%20FINDINGS.PDF?courtCode=30&di=4176115). However, in a motion to strike him as a witness, the state argued that “due to Dr. Rose’s limited availability and his long windedness, the State’s deposition of Dr. Rose remains incomplete. Defense counsel has failed to provide dates in which Dr. Rose’s deposition can be completed” (from https://www.courts.mo.gov/fv/c/Mot%20Strike%20Depo%20Dates.pdf.PDF?courtCode=30&di=4184443). Further, from the same motion, “Defense counsel has advised the State that they do not plan on trying this case. This is evidenced in their delay tactics with the Court’s scheduling order.” So, in one motion, Dr. Rose was apparently part of the groundwork for a not guilty by reason of insanity plea, but he was so unavailable (and long-winded) that the State moved to strike his testimony as a witness as no more more than part of a stall tactic so that the defense did not have to try the case.
The biggest problem, though, turned out to be someone who would become a defense expert, Dr. Tahir Rahman. In January 2021, he argued Kourtney Aumen was competent to stand trial (https://www.courts.mo.gov/fv/c/JUDGMENT%20FINDINGS.PDF?courtCode=30&di=4176115). In fact, he estimated her IQ was between 70 and 90, which would be an IQ in the low-normal to normal range and fail to meet the first criteria for an Intellectual Disability – Mild diagnosis. However, in July 2026, he argued she was incompetent and had an intellectual disability – mild (https://www.courts.mo.gov/fv/c/Finding%20of%20Fact%20and%20Conclusions%20of%20Law.PDF?courtCode=30&di=4168941). It is worth noting that, unlike adaptive functioning, IQ scores tend not to vary a great deal in an adult. However, apparently, Dr. Rahman only estimated her IQ the first time; there was (maybe) not an actual IQ assessment done.
Dr. Rahman is a board certified psychiatrist who is known for his work on cancer psychiatry (particularly the effects of psychiatric medications on cancer and well-being), as well as proposing the idea of “Extreme Overvalued Beliefs” as a motivation to criminal acts; these beliefs, according to Dr. Rahman are not delusions, which are a sign of psychosis and potential insanity, but shared, strongly held beliefs, which might instead affect competency. On the basis of Dr. Rahman’s testimony, on September 11, 2026, Case.Net shows a proposed finding that Court held Kourtney Aumen was not competent to stand trial (https://www.courts.mo.gov/fv/c/Finding%20of%20Fact%20and%20Conclusions%20of%20Law.PDF?courtCode=30&di=4168941).
However, in the second “scolding” (a finding), the State completely tore Dr. Rahman’s testimony apart (https://www.courts.mo.gov/fv/c/JUDGMENT%20FINDINGS.PDF?courtCode=30&di=4176115). They pointed out that his testimony in 2026 about his 2021 competency evaluation completely contradicts his actual 2021 competency evaluation report. They pointed out that only 1 – 2% of his practice dealt with forensic issues, with this being his only competency case since 2017. They pointed out that he did not ask anything about malingering (or lying) on the part of the defendant, which all forensic assessors have to consider as a possibility. They then pointed out that he did not consider the possibility of anti-social personality disorder or borderline personality disorder, which had been raised as possible diagnoses in a NGRI examination in January of 2026. (Oops…by the way, those are not helpful diagnoses if you want to claim your client is a victim who is not guilty by reason of insanity. They absolutely are something that should be considered if you want to determine if your client is lying to you as part of a competency evaluation.)
Then the kicker(s). They point out that Dr. Rahman did not include 6 questions of a competency assessment that Kourtney Aumen answered correctly in his report. All 6 show that she understood the trial process, particularly when added to the questions she got correct that he did include. (He included 8, most of which she also got correct.) Why didn’t he include those last 6 – all of which she answered correctly? “Dr. Rahman testified at the evidentiary hearing that he omitted those questions to keep his report brief, despite the purpose of the report being competency. However, Dr. Rahman had no concerns with brevity when discussing extreme overvalued beliefs” (https://www.courts.mo.gov/fv/c/JUDGMENT%20FINDINGS.PDF?courtCode=30&di=4176115).
They also point out that, during her competency assessment with another qualified evaluator (emphasis on qualified in the finding), Dr. Harrop, (1) Kourtney Aumen understood the possibility of not guilty by reason of insanity, (2) found the idea of a trial for first degree murder scary, (3) felt that a trial for a lesser charge, like child endangerment, would be OK because she had already served 4 years, (4) acknowledged they had a strong case against her, and (5) that she had a pretty good chance of being found guilty (https://www.courts.mo.gov/fv/c/JUDGMENT%20FINDINGS.PDF?courtCode=30&di=4176115). Whew…that one was a doozy.
So, with that, Kourtney Aumen is declared competent to stand trial (https://www.courts.mo.gov/fv/c/JUDGMENT%20FINDINGS.PDF?courtCode=30&di=4176115); has her motion for a bench trial, instead of a jury trial, denied (https://www.courts.mo.gov/fv/c/DENY%20WAIVER%20OF%20TRIAL.PDF?courtCode=30&di=4186613); and decides to accept a plea deal, by pleading guilty to two of the charges against her: second degree murder and first degree assault (https://www.courts.mo.gov/fv/c/DOCKET%20ENTRY.PDF?courtCode=30&di=4190965). The trial date (Oct 26, 2026) has now been cancelled and sentencing was scheduled for Dec 21, 2026.
The charges against Kourtney Aumen originally included first degree murder, child abuse, child endangerment, assault, and armed criminal action. With her plea, she is pleading to second degree murder and first degree assault. However, over the past 6 years, she and her attorneys have used a variety of stalling tactics and had a defense expert behave so inappropriately that he tried to conceal information from his reports and testimony.
The majority of evaluations did find that she had Intellectual Disability – Mild, but, as can be seen in the end result, that is not an automatic “sentence” of incompetent. From a legal psychology curiosity standpoint, I can be curious about those potential diagnoses of antisocial personality disorder or borderline personality disorder, along with how Dr. Rosario would have explained how anyone, regardless of IQ, can influence others. I can also be curious about whether or not Kourtney Aumen received the supports she needed as a child to live her most independent, functional life as an adult.
But, there is no sustained evidence presented that shows Kourtney Aumen as a victim; in fact, everything shows her as an active, voluntary participant in the abuse of 2 children (and their parents). One of those children died; the other child and their mother had to be hospitalized. There were no markings on Kourtney Aumen (https://www.courts.mo.gov/fv/c/JUDGMENT%20FINDINGS.PDF?courtCode=30&di=4176115). The motions and findings show that this process has taken 6 years due to the actions of the defense and that Kourtney Aumen understood the trial process (was competent to stand trial), even though one of the defense witnesses testified otherwise. And, upon hearing that there would be no more competency hearing delays and no bench trial, Kourtney Aumen decided to enter a guilty plea, with sentencing for herself set for Dec 21, 2026. Sentencing for the other 3 co-defendants will likely be scheduled in the coming days/weeks as well, as the resolution of Kourtney Aumen’s guilty phase will allow for all co-defendants to be sentenced.
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