There is no known official record of the date or place of birth of Bonney. A Catherine McCarty, believed to be Bonney's mother, married William H. Antrim, of Indiana, in the Presbyterian Church in Santa Fe, NM, on March 1, 1873. Witnesses included Henry McCarty and Joseph McCarty, 'presumed' to be sons of the bride.
The Guthrie song in Lomax is nonsense. Billy had several Mexican (Hispanic) friends and girlfriends, and could speak at least some Spanish.
Names applicable to Billy were William Henry Antrim, William H. Bonney, William H. McCarty - depending on step-fathers and Billy's own preference.
His (using the name Henry Antrim) first killing was in a (presumed drunken) fight in Camp Grant (now in AZ), near Silver City, NM, 1877 (inquest by a J. P. and six jurors). Billy ran to the silver mining town of Georgetown, where he took the name William H. Bonney (some speculate that this was his mother's name).
The story of Billy is a sad one, that of a young man on the losing side of a war between an English rancher- mercantile entrepreneur and a ruthless buccaneer gang aiming to take over. The killing of the Englishman, John H. Tunstall, Billy's employer, sparked a chain reaction of murders in what is known as the Lincoln County War. General Lew Wallace, Governor of the Territory (author of "Ben Hur"), who deferred governance to others, became involved. Wallace's part in the affair primarily was his unsuccessful "Amnesty Proclamation" of 1878, repudiated by another player, the commander at Fort Stanton. Col. N. A. M. Dudley was indignant about a clause extending amnesty to officers in the Army who had become involved (he was one).
The story is long and involved, so complex that it is difficult to comprehend and would be considered improbable if it appeared in a novel.
Billy was convicted of murder and sentenced to death in 1881, case No. 411, U, S. A. vs. Charles Bowdry, et al., for the killing of "one Roberts, against whom they had shot bullets, on the Mescalero Indian Reservation..." This sparked the escape, and further murders by Billy.
See: William A. Keleher, 1957, "Violence in Lincoln County 1869-1881," University of New Mexico Press. A balanced view, with many court records and newspaper reports.