Pat Garret's descendants are against it. Gov Richardson's possible justification for this pardon rest upon past history such as this:
"Historical documents show that Mr. Wallace struck a deal with the Kid that if he would testify before a grand jury about a killing he had witnessed, the governor would grant him a pardon for his many crimes. Billy the Kid did testify but the pardon never came, something the outlaw grumbled about as he managed to escape the law, get caught and then escape again, only to be gunned down in the dark by the frontier lawman in 1881."
This is former governor of New Mexico, Lew Wallace, who also is the author of the enormously popular novel, at least for many decades in the past, Ben-Hur: A Story of the Christ. Which is how we came to have still famous Charleton Heston chariot race in the Colisseum.
History lives, yay history!