The Department of Justice has a "roll call" page listing federal marshals and possemen who died in the line of duty to "honor their memory and their sacrifice". The list includes at least two men who died while trying to capture fugitive slaves in the 1850s. Edward Gorsuch, the second entry on the list, was a slave owner killed while trying to capture six of his fugitive slaves. From the Maryland State Archives:
Gorsuch received a letter from William Padgett, a farm worker in Lancaster County, Pennsylvania, saying that he knew where his slaves were hiding. Gorsuch gathered some of his family members and local whites and headed to Pennsylvania via train. Once in Philadelphia, they met up up with Deputy Federal Marshal Henry Kline, completed the necessary paperwork, and then continued in pursuit of the escaped slaves. On September 11, 1851, as Gorsuch, his party, and Padgett were making their way to capture the slaves. Early on they were spotted by one of the slaves, who then hid in the home of William Parker, a known Black abolitionist in Christiana, a small town in Lancaster County. Parker met Gorsuch and his party at the door and refused to give the slaves up. As Parker confronted Gorsuch, Parker's wife Eliza opened a second floor window and blew a horn, which was an alarm for local African Americans. She was shot at (but not hit) by a member of Gorsuch's entourage, but not before townspeople armed with guns and various weapons responded to the alarm. Gunfire was exchanged, and Gorsuch's son, Dickinson, was badly wounded but managed to flee to a nearby cornfield. Edward Gorsuch himself was killed. Thirty-six Blacks and five white men were indicted for high treason against the United States as a result of the so-called 'Christina Riot.' All of the defendants were found not guilty.
The third man on the DOJ list, James Batchelder, was a courthouse guard killed while trying to prevent the rescue of a fugitive slave. From the description of an illustration depicting the return of the slave (pictured above), via Harvard:
In May of 1854, slave catchers captured Anthony Burns in Boston. While held at the courthouse, an abolitionist mob led by Lewis Hayden, Thomas Wentworth Higginson, and others attempted to rescue the fugitive by battering down the doors with a fence rail. In the melee, a pistol shot struck and killed James Batchelder, one of the courthouse guards. In response, a large contingent of soldiers escorted Burns out of Boston and back into slavery which triggered a massive abolitionist protest.
The law, right or wrong.
JD Tuccille wrote about a similar fugitive slave case in explaining why he teaches his child its ok to break the law sometimes.
h/t the anonymous Eduard van Haalen