“I expect you have forgotten what you promised me,” Billy the Kid wrote to New Mexico Territory’s governor, Lew Wallace, in 1881. The Kid was writing from a Santa Fe jail cell. He was there because of the dogged efforts of Pat Garrett, who had been elected sheriff of Lincoln County, which comprised the southeastern part of the territory, on the promise that he would put a stop to Billy and his gang of rustlers. Now Billy was waiting to be transported to Mesilla, where he would be tried for the murder of another Lincoln County lawman, Sheriff William Brady.

Billy’s pointed reminder to Wallace referred to a deal the two had made two years earlier. Wallace had promised to grant Billy amnesty for his role in shooting Brady and other misdeeds if the Kid agreed to testify before a grand jury investigating another Lincoln County murder. Billy held up his end of the bargain, but the governor failed to follow through with his. The Kid’s letter went unanswered, as did all the others he sent to the Palace of the Governors on Santa Fe Plaza.

Although the Kid had not acted alone in the Brady killing, he was the only one to be tried and convicted of the crime. From Mesilla, he was transferred to Lincoln to await the day of his hanging. With no sign of the promised pardon, the Kid staged the most famous of his many daring escapes. On April 28, 1881, while Garrett was away collecting taxes, Billy surprised his two guards, killing both deputies with their own guns. As the townspeople watched in horror and awe, the Kid rode away unmolested.

Once more, Garrett had the dangerous job of hunting down the outlaw, and he knew that when they eventually met, only one would walk away, for Billy had let it be known that he would not be taken alive again. Tipped off that the Kid was at Ft. Sumner, where his sweetheart lived, Garrett rode to the Pecos Valley with two deputies. About midnight on July 14, Garrett shot and killed a surprised Billy in the bedroom of rancher Pete Maxwell’s house.

Garrett was lauded for bringing to an end the bloody career of the 21-year-old, but the sheriff would live to see his popularity reversed with Billy’s. The Kid quickly became an outlaw hero and Garrett the villain who shot him down in the dark.

What might have happened if Wallace had kept his bargain? Chances are, Billy would have continued to take — and commit occasional mayhem — as he pleased, but the romanticist in all of us likes to imagine a different outcome.

In 2003, New Mexico Gov. Bill Richardson announced that he would consider making good on Wallace’s promise and issue a pardon for Billy. Richardson’s announcement came in the midst of international media attention over a modern-day forensic investigation looking into the circumstances of the Kid’s death. But as the hoopla subsided, so did the talk of a pardon.

Now the governor, whose term expires in January, is reportedly again giving serious consideration to Billy’s pardon.

Just what would a pardon for Billy the Kid mean? It can no longer help the Kid, of course, whose body lies buried beneath a stark metal cage at Ft. Sumner. Richardson would certainly make headlines, but after that would Billy lose some of his outlaw mystique? Would Garrett’s obsession be made ridiculous? Would the two deputies killed during Billy’s sensational daylight jailbreak have died in vain?

A wronged man or not, Billy the Kid was a cattle rustler and a stone-cold killer, a notorious criminal singlehandedly responsible for the deaths of four men (there were more victims, but Billy had help with them). Yet he has been featured in more than 60 movies and hundreds of publications. We love Billy, or, rather, what he has become in our imaginations. Such are the benefits of mythology.

Still, regardless of Billy’s crimes, the motives of Richardson or the hollowness of posthumous justice, it all comes back to Wallace’s promise. A deal is a deal, and 129 years doesn’t change that. Billy is owed a pardon.

Richardson has a few more months to decide, and it may be the Kid’s last chance for a long time to come. No matter what happens, though, Billy the Kid’s place in history is secure. It’s one sentence he’ll never escape.

Mark Lee Gardner is the author of “To Hell on a Fast Horse: Billy the Kid, Pat Garrett, and the Epic Chase to Justice in the Old West,” which was published in February.