We now know that the day after he was shot, he was scheduled to testify against fellow officers in a racketeering trial:

Last Wednesday, Detective Sean Suiter, along with an as-yet-unnamed partner, were in the West Baltimore neighborhood of Harlem Park. Suiter’s usual partner in the homicide unit, Detective Jonathan Jones, was off that day.

The police version of what happened, as relayed to the Baltimore Sun, goes like this: The detectives were looking for a witness to an unsolved triple homicide case that is nearly a year old when they spotted “suspicious activity” nearby. Suiter and his backup partner split up to cover different exits of the block. Suiter then confronted a man, who shot him in the head after the detective tried to speak. Suiter, an 18-year veteran of Baltimore’s police force, and a 43-year-old married father of five, was pronounced dead a day later, becoming the city’s 309th murder victim of 2017.

………

The neighborhood was promptly put on lockdown. Over the course of the week, the reward fund to find Suiter’s killer climbed to $215,000 – a figure experts think might be a state record. The Harlem Park neighborhood lockdown was justified as a way for cops to preserve the crime scene and collect evidence.

………

Six days after the murder, The Baltimore Sun reported that the city was entering “uncharted territory” for the police department, which usually apprehends police killers shortly after the fact. The longest it’s taken Baltimore police to do so over the last five decades was five days, in 1985. In that instance, the suspect had fled to Oklahoma.

………

The rumor that had been circulating through the neighborhood was that Suiter was preparing to testify against some of the seven officers indicted for racketeering charges in March. An eighth was indicted in August and a ninth last week. (The charges were filed by former U.S. Attorney Rod Rosenstein, a month before he was named Deputy Attorney General in Trump’s Department of Justice. It was there he would have his moment in the historic sun. After Trump blamed him for firing FBI Director James Comey, he appointed special counsel Robert Mueller.)

A spokesperson for the current U.S. Attorney for Maryland told The Intercept on Monday that they could not comment on whether or not Suiter was planning on testifying in their case. But on Wednesday evening, Commissioner Davis confirmed that Suiter was in fact set to testify before a grand jury that Thursday, a day after he was shot. He also said that Suiter appeared to have been killed by his own weapon after a struggle.

(emphasis mine)

Despite the ubiquitous radio reports, I hadn’t been following this case particularly closely, but it has suddenly become much more interesting.