The most relevant part of the article:

In 2019, Gardner added [St. Louis police detective Roger] Murphey to a list of police officers who would not be allowed to apply for criminal charges because of questions about their credibility, and she said her office would evaluate whether those officers could testify in court. Although the identities of those officers were not made public, one of Murphey’s supervisors notified him that his name was on Gardner’s list.

Weeks later, a prosecutor in Gardner’s office notified Murphey that the office not only would actually let him testify in the cases he had led that were heading to trial — it expected him to.

Murphey, who retired in September 2021, said he felt stuck in a Catch-22. If Gardner was going to impugn his character and question his credibility, he decided, he wouldn’t cooperate with her prosecutors. He believed that if he went to court, defense lawyers would use his inclusion on Gardner’s list to attack him on cross-examination, making the trials more about him than the defendants.

Since that time, he has refused to testify in at least nine murder cases in which he served as lead detective. He said he told prosecutors that, if they subpoenaed him to testify, “I’m going to sit on the stand and I’m not going to answer any questions.”

My response is…

First of all, how would defense lawyers know he was on the list if the list wasn’t made public? This seems like an obvious lie to me. He wasn’t stuck in a Catch-22. This was not about the outcome of the trial, but about him getting revenge for the prosecutor essentially ending his career of arresting criminals. He’d probably be stuck with a desk job or something like that.

He was mad that his past actions had finally caught up with him, but blamed the person who finally held him accountable. It’s not like the prosecutor was randomly adding names to the list of officers without credibility.

And if you needed any proof to back up his character, it’s that he was willing to let nine murderers go free in revenge. Nine deaths he was willing to let the murderer get away for personal reasons. It sounds like the prosecutor made the right call.