The defense they eventually decided on would change the course of history: they argued that the State of Oklahoma could not prosecute McGirt because he was a Native American and the crime occurred within the historic boundaries of a tribal reservation.
Attorneys for the state dismissed this claim as ridiculous, but the history and the law proved to be more complex.
In the 1800s, the U.S. government forced many Native American tribes from their ancestral homes during the barbaric Indian Removal, relocating them to new lands. Through treaties, the tribes were promised the right to these new lands through the creation of Indian reservations. This collection of reservations became known as Indian Territory.
Following statehood in 1907, it was assumed these reservations in Indian Territory ceased to exist. Over a century later, this assumption proved to be very wrong.
In the McGirt case, the Supreme Court determined that the historic Muscogee (Creek) Reservation still exists because Congress never dissolved it.