A small contingent of soldiers entered a large Sioux camp to apprehend an individual accused of killing a migrant's cow, despite the fact that such issues were supposed to be resolved by the US Indian agent according to treaty agreements.

On August 17, a cow belonging to Mormon Christian J. Larsen (chaplain of the Hans P. Olsen Company of Danish immigrants) traveling on the nearby Oregon Trail, strayed and was killed by a visiting Miniconjou (Sioux) named High Forehead.

"[4] Lt. Hugh Fleming, the senior officer of the small garrison, consulted with the chief, Matȟó Wayúhi, also known as Conquering Bear, to discuss the loss of livestock.

Lt. Fleming was either unaware, or chose to ignore that these matters were supposed to be handled by the local Indian agent according to the terms of the Treaty of 1851.

Lt. Fleming asked the Sioux to arrest High Forehead and deliver him to the fort, which Conquering Bear refused; he had no authority over the Miniconjou and did not want to violate his people's tradition of hospitality.

A commander at Laramie later recalled, "There is no doubt that Lt. Grattan left this post with a desire to have a fight with the Indians, and that he had determined to take the man at all hazards.

"[7] In Grattan's party were a sergeant, a corporal, 27 privates, and a French-Indian interpreter named Lucien Auguste; the military forces had two artillery pieces in addition to arms.

Bordeaux reportedly said the interpreter Auguste taunted the Sioux, and failed to fully or accurately translate Conquering Bear and Grattan's comments, as there seemed to be confusion between them.

[9] The Sichangu Sioux warriors, led by Spotted Tail, then a rising war chief within their people, quickly killed Grattan, 11 of his men, and the interpreter.

[10] A group of some 18 soldiers retreated on foot trying to reach some rocks for defense, but they were cut off and killed by overcoming warriors led by Red Cloud,[citation needed] a rising war chief within the Oglala Sioux.

On the third day after the US attack, the Sichangu and Oglala abandoned the camp on the North Platte River and returned to their respective hunting grounds.

[13][14] The soldiers' remains were later exhumed (unburied) and re-interred at Fort McPherson National Cemetery, where a white marble monument was erected in their memory.

"[citation needed] Accounts generally ignored the US soldiers' instigation of the event by their failures: first, to leave it up to the Indian agent to settle, as called for in the treaty; and second, shooting chief Conquering Bear in the back.

"[citation needed] Warned by Thomas S. Twiss of the Indian Bureau that the army had put a force in the field, half of the Lakota who were camped north of the Platte River went into Fort Laramie for protection as "friendlies".

[17] To make the Sichangu Women and children free, Harney claimed the delivery of the leaders of Grattan Fight, and Spotted Tail, Red Leaf (Waba Sha), Long Chin (Iku Hanska) and, some days later, Standing Elk (Hehaka Najin) and Red Plume (Wiyaka Sha), went to Fort Pierre, esorted by Iron Shell and the whole Sichangu crowd.

[18] On October 25, the three warriors sought by the expedition surrendered, were held for a year at Fort Leavenworth (where Spotted Tail was reached by his wife several months later), and were released.

[19] Others suggest numerous factors, especially US desire for control of lands that were Sioux territory, that contributed to make warfare inevitable.