Ok. First of all Paris District was not established until March, 1889 so that is not where he was assigned. Here is the full story on Erwin:

William Erwin, died April 13, 1886. According to Robert Ernst’s excellent book, “Deadly Affrays, The Violent Deaths of the US Marshals,” p.75ff, Erwin was appointed a deputy by Marshal John Carroll of the Western District of Arkansas [Fort Smith] on January 1, 1886.
A notorious horse thief by the name of Felix Griffin was arrested by a Cherokee lawman who turned the man over to Erwin. Griffin and Erwin then left Webbers Falls bound for the Fort Smith, Arkansas federal jail, a trip of about 65 miles. The pair crossed the Arkansas River on Squirrel Field’s ferry. A few hours later, two other all around bad guys, Frank Palmer and Jack Spaniard, used the same ferry. About sunset gunshots were heard in the Pheasant Bluff area. The following morning, residents found a saddled horse grazing nearby. Shortly after the body of Erwin was discovered, killed by rifle fire ambush. His guns were still in their holsters. About a year later Felix Griffin was shot and killed while attempting to steal horses. Two years after Erwin’s killing, Jack Spaniard was captured. He was tried during the April, 1889, court session and was sentenced to hang. On August 9, 1889, Spaniard went to the gallows. Frank Palmer was never found.