Forensic psychiatrist says Marion man didn’t know right from wrong when he killed ex-girlfriend

CEDAR RAPIDS — A Chicago forensic psychiatrist testified Monday that a Marion man on trial for killing his ex-girlfriend in 2017 was suffering from an acute, psychotic state and had a “skewed sense of reality with grandiose ideas,” which made him unable to distinguish right from wrong when he stabbed the woman.

Greg Davis had been using illicit substances since he was a youth, including marijiuna, alcohol, opioids, cocaine and then methamphetamine, Dr. Scott Gershan, assistant professor of psychiatry at Northwestern University Feinberg School of Medicine in Chicago, said during his testimony for the defense.

Davis’ meth use began to escalate in 2017 and was at its peak Sept. 28 through Oct. 2, when his former girlfriend, Carrie Davis, 29, died.

Gershan said Davis had psychological issues growing up. He suffered from anxiety disorder and social anxiety disorder and was treated for substance abuse, but he didn’t receive adequate treatment for his psychological problems.

When he was using meth “heavily,” it started to trigger concerns about mental issues, and his family noticed “behavioral disturbances.”

Insanity defense

In his defense, Davis is claiming insanity. Iowa law requires a defendant using that defense to prove he was suffering from a diseased or deranged mental condition that rendered him incapable of knowing the nature and quality of an act or incapable of distinguishing between right and wrong.

Davis, 30, is being retried in Linn County District Court on a first-degree murder charge.

According to testimony, Davis, after stabbing Carrie Davis 26 times on Sept. 28, 2017, concealed her body in a roll of carpet and left her on a utility trailer outside a vacant rental house owned by Davis’ parents. Police found her body Oct. 2.

A Linn County jury convicted Davis in 2018. He was granted a new trial in 2020 when the Iowa Supreme Court overturned the jury conviction. The justices, in a 4-3 opinion, ruled the trial judge erred by not including an instruction to the jury on Davis’ insanity defense.

In this trial, Davis waived his right to a jury trial, choosing a bench trial — meaning 6th Judicial District Judge Sean McPartland will determine the verdict. The trial started last Tuesday.

Role of meth

The defense also is arguing that the multiple stabbing injuries weren’t the cause of Carrie Davis’ death. Instead, the high level of meth in her system killed her, and she was already dead when Davis stabbed her, according to defense expert testimony.

Gershan said he agreed with another expert who testified last week that Davis suffered from meth-induced psychosis.

Assistant Linn County Attorney Mike Harris asked if Greg Davis’ use of meth was a voluntary act, and Gershan agreed.

Harris asked if Davis had any substance abuse treatment after 2010. Gershan said he wasn’t aware of any.

Harris said some of the information about Davis’ substance use and psychological problems came from his parents and from Davis himself, who aren’t neutral sources, and that Davis may be “motivated to lie or embellish” details.

Gershan agreed.

Gershan also admitted Davis wasn’t diagnosed with psychosis before he was charged with murder.

Judge McPartland asked if he considered taking a drug a voluntary act, as another expert had testified. That expert said meth-induced psychosis didn’t qualify for insanity because taking the drug is voluntary.

Gershan said taking meth alters brain chemistry, which drives behaviors in a different way and would affect someone’s decisions.

A neuro pharmacology expert said the meth in Carrie’s system — 4,700 nanograms — was sufficient to cause death.

However, Craige Wrenn, a professor and chair of Pharmaceutical and Administrative Services at Drake University, said he wasn’t qualified to determine Carrie Davis’ cause of death, but the amount of meth in her system was enough to result in death for most people.

Wrenn also admitted that cause of death can’t be solely based on toxicology.

The defense will wrap up its case Tuesday, and the case will be submitted to the judge, likely on Wednesday.

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