The Lincoln County War was begun when a posse of men, deputized by Sheriff William Brady, murdered young Englishman John Henry Tunstall on February 18, 1878. The posse had ostensibly been chasing Tunstall in order to attach some stock Tunstall and his men were driving from Tunstall's ranch on the Feliz River to Lincoln, but the posse's real motivation was clear -- eliminate John Tunstall as an economic threat to businessmen James Dolan and L.G. Murphy, who had Sheriff Brady in their pocket.
Naturally, Tunstall's murder did not sit well with his friends and employees (among them, a young cowboy known then as "Kid Antrim" and known to us now as "Billy the Kid"). These men banded together and called themselves "The Regulators," as they meant to regulate justice against Murphy and Dolan's men.
On April 1, 1878, in the town of Lincoln, six Regulators (Billy the Kid, Jim French, John Middleton, Frank McNab, Fred Waite and Henry Brown) were eating breakfast inside the Tunstall store after having spent the night sleeping within the protection of the store's fortress-like, thick adobe walls. They had spent the night there with Tunstall's former clerk, Sam Corbet, and the odd, self-aggrandizing Robert Widenmann who was a Regulator and had been with Tunstall and the rest of his party on the day of his death. Widenmann had proven his bad judgement on a number of occasions, and in his letters to those not directly involved in the Lincoln County War, always portrayed himself as the hero in any situation (when he was clearly a liability to the Regulators more than an asset).
Suddenly, one of their number saw Sheriff William Brady and four of his deputies walking down the street toward the courthouse. (It should be noted that the courthouse at that time was a building now referred to as the "Convento", located east of the Tunstall store. It was not the modern-day courthouse, which at that time was still owned by James Dolan and business partner John Riley).
According to survivors, the sheriff and his men were on their way to tack a notice onto the courthouse but they were all extremely well-armed (although I cannot imagine trying to go buy a quart of mil during the Lincoln County War without carrying a .45). This explanation for why they were on the street that day is one of several.
There are a few possibilities regarding why the Regulators decided to ambush the sheriff and his men. One is that they were out for spontaneous revenge. Another is that either McSween ordered the killing, or the killing was made to protect McSween from arrest and murder at the hands of the sheriff. In any case, before the day was through, William Brady's wife would be a widow, pregnant with their ninth child.
from the Lincoln County Historical Society newsletter, Summer 2010