Slave cases are still cited as good law across the U.S. This team aims to change that

This story starts — but certainly doesn't end — in 19th century Maryland, when John Townshend updated his will.

Townshend grew convinced at the end of his life that God would punish him if he did not free the enslaved people he owned and give them all of his property. But Townshend's relatives challenged his final wishes in court, arguing that his decision had been the result of a delusion.

That 1848 case was the first U.S. appearance of what became known as the "insane delusion rule," which remains grounds for contesting wills to this day. And Townshend v. Townshend itself has been cited in at least 70 other cases across the country — from New Hampshire to California — over the years, as recently as 2007.

It's one of thousands of cases involving enslaved people that lawyers and judges continue to cite as good precedent, more than a century after the 13th Amendment abolished slavery in the U.S.

Justin Simard, an assistant professor at Michigan State University's College of Law, estimates there are about 11,000 such cases out there — and about one million more that use them to back up their arguments.

"I've done some analysis just with a sample of cases and concluded that 18%