Maryland officials say they’re launching an investigation into in-custody death reports produced during the tenure of Dr. David Fowler, a former top medical examiner for the state who served as a key witness for the defense in the Derek Chauvin trial.

Fowler was Maryland’s chief medical examiner from 2002 to 2019. Chauvin was convicted of murdering George Floyd in 2020 and the ex-police officer is awaiting sentencing.

Maryland Attorney General Brian Frosh and Gov. Larry Hogan announced the investigation on Friday after they received a letter signed by 431 doctors saying Fowler’s conclusions during the Chauvin trial were so unusual that they raised questions about his previous work.

“Dr. Fowler’s stated opinion that George Floyd’s death during active police restraint should be certified with an ‘undetermined’ manner is outside the standard practice and conventions for investigating and certification of in-custody deaths,” the letter said. “This stated opinion raises significant concerns for his previous practice and management.”

Fowler testified that Floyd’s death was caused not by Chauvin kneeling on his neck for nine minutes, but by a sudden cardiac arrhythmia stemming from a preexisting heart condition, combined with narcotics, exposure to fumes from a police vehicle, and a benign tumor found on Floyd’s pelvis after his death. Other medical experts who testified during the trial contradicted Fowler’s assessment.

The families of three Black men who died in police custody in Maryland have urged a review of Fowler’s work for years, saying his office reached questionable conclusions that police were not responsible for their deaths, the Baltimore Sun reports.

“We have been trying to get someone to listen, someone to care. We weren’t taken seriously, and all other families weren’t taken seriously as well,” Latoya Holley, whose 19-year-old brother Anton Black died in Maryland in 2018 after police sat on him for more than six minutes, told the Sun.

Fowler’s office was also responsible for reports whose conclusions didn’t favor police, including an assessment of the death of Baltimore teenager Freddie Gray in 2015 that ruled it a homicide. The officers involved were ultimately acquitted.

A spokesperson for Frosh told the Sun she couldn’t explain why Fowler’s work hasn’t come under invesitgation before, but that his office is “willing to take on the review” now.

Fowler defended his tenure to the paper, saying “There’s a large team of forensic pathologists, with layers of supervision, and those medical examiners always did tremendous work.”

Naomi Starobin contributed to this report.