Dr. Patrick Henry Cronin was with a patient on the evening of May 4, 1889, when a stranger arrived at his Near North Side office begging for help. As soon as Cronin was free, the anxious visitor told him that a worker had been injured at a Lakeview icehouse. The doctor hurried into a waiting buggy and headed off.

He wasn’t seen again until almost three weeks later, when police pulled his decaying body from a sewer basin at Foster and Broadway.

Suspicion in the murder case immediately centered on Cronin’s rivals in Clan na Gael, a secret Irish nationalist group whose members included some of Chicago’s leading politicians and much of the police force. The investigation and trials that followed attracted international press coverage, turning the slaying into one of the most sensationalized crimes of the 19th century.

It also offered a window into the injustice and political corruption of the age. In Blood Runs Green (University of Chicago Press), author Gillian O’Brien takes a fresh and compelling look at the case, exploring its origins in a disastrous dispute among Irish nationalists over how to fight the British oppression of their homeland.

Half a century after the potato famine in Ireland, waves of immigration had made Chicago “the center of Irish republicanism” in the United States and home to the leaders of Clan na Gael. But the group was fragmenting over tactics. One faction favored radical action known as the “dynamite policy”—attacking public spaces in Britain, including an 1885 bombing of the Tower of London and House of Commons. Arguing that such violence only hurt their cause, the other camp favored advancement through traditional political means.

Leading the radicals—at least when he saw a personal advantage in doing so—was longtime Clan leader Alexander Sullivan, a political operator with a violent past. He’d once killed a school principal who’d made disparaging comments about his wife, Margaret, a leading journalist in Chicago. Yet Sullivan helped deliver the Irish vote at election time, and after being appointed secretary of Chicago’s board of public works, he controlled lucrative contracts and scores of patronage jobs.

On the other side of the Clan fight was Cronin, a respected physician who emerged as a leader of the faction calling for reforms and accusing Sullivan of stealing from the Irish cause. When Sullivan’s allies spread the lie that Cronin was a British spy, the doctor began to worry that his life was in danger.

He was right. But from whom, exactly?

Spoiler alert: three members of the Clan and a criminal associate were eventually convicted, but the homicide investigation and subsequent trials were deeply flawed. More than anything else, they succeeded in revealing extensive corruption in the police department and courts.

As O’Brien documents, the standards of the press were no better: while some reporters aided the pursuit of justice, many publications reinforced stereotypes of Irish immigrants as stupid and violent, going as far as running cartoons depicting them as apes.

O’Brien shows that the facts of Dr. Cronin’s murder are buried under layers of truth and untruth. As she digs deeper, O’Brien, a lecturer at Liverpool John Moores University, sometimes shares so many details about so many characters that the narrative slows. But that’s a small gripe about a provocative work.

In the end, O’Brien concludes that no one won: the killing of Dr. Cronin crippled the Irish cause on both sides of the Atlantic. Under heightened suspicion, republican groups struggled to raise funds and overcome internal ruptures.

The book left me thinking about even broader questions. Amid our latest national debates on race and justice, I wondered if anything has fundamentally changed about our appetite for heroes, villains, and instant judgments. When we’re repeatedly shown images of what a criminal is supposed to look like, it becomes harder and harder to accept any other story line.