Escape!
Billy the Kid once used the epigram, 
“There’s many a slip, ‘twixt the cup and the lip”
It’s an old saying, meaning don’t count your chickens before they hatch. It’s that even when a good outcome or conclusion seems certain, things can still go wrong.

The Kid had been sentenced to death on April 13 and was given 30 days to repent, as he was due under the noose on the 13th of May 1881. After Billy was transferred to Lincoln County jail from Mesilla, he found himself in the old Murphy Store chained and shackled in Murphy’s old bedroom on the second level.
On the floor, a line of chalk divided the room. If The Kid crossed the line at any time he was to be killed, keeping him up against the walls in the northeast upper corner of the building. Some reports suggest he was chained to the floor as well. In Murphy’s old living quarters on the 2nd level, was Garrett’s office. In the rear of Garrett’s office was Billy’s room, which had two windows.

The North window overlooked the front of the building and the East window had a view looking down the road. The Kid’s room was directly above the post office. Across the hall was Murphy’s old housekeeper’s room, where 5 prisoners from Tularosa were locked in.

Billy’s guards had been chosen by Sheriff Garrett, and were not in any way pals of Billy. These 2 men were J.W. Bell and Bob Olinger. Bell was decent mannered to Billy, even though Bell’s friend James Carlyle was killed while serving as part of Sheriff Hudgen’s posse during a standoff against Billy’s crew at the Greathouse station.
Ollinger was a Dolan henchman who previously rode with the Seven Rivers Warriors gang. Bob Ollinger was convinced Billy had killed his friend Robert Beckwith during the 5 day battle in Lincoln and held a grudge since they were on opposite sides of the Lincoln County War.
But Ollinger had earlier killed John Jones, who was a close friend of Billys. Word has it that Billy promised John’s mother that he would avenge her son’s death.
At the big house in Lincoln, Sheriff Garrett warned his deputies about the dangers of Billy’s innocent demeanor:
“You think of yourself as an old hand at this business, you have guarded many prisoners and faced danger many a time apprehending them, and you think you are invincible and can get away with anything…
But I tell you as a good man you are, that if that man, is shown the slightest chance on earth, if he is allowed the use of one hand or is not watched at every moment from now until the moment he is executed, he will affect some plan by in which he will murder the whole of you before you even have time to suspect that he is any such intention.”
Billy had been mostly alone in the closed room. He sat in his window day and night, watching Lincoln’s days go by. Occasionally playing a little game of Monte with Bell, who seemed to take a liking to The Kid. As for Ollinger, he would taunt Billy with his shotgun whenever he could and often dared him to try and escape. He hated the Kid and the kid hated him.

Garrett reflects,
“There existed a reciprocal hatred between the two, and neither attempted to disguise or conceal his antipathy for the other.”
Billy quietly observed the deputies’ routines and at about 5 p.m. each day Sam Corbett, a former employee of Tunstalls, would bring Billy a plate of food just as Ollinger would escort the Tularosa prisoners to Worley’s for dinner.
A friend of Billy, Mrs. Anne Lesnett reportedly visited Billy in jail and brought him something to eat. The guards allowed the visit. While she was there Bob Ollinger invited Mrs. Lesnett to watch the hanging.
The joke made her sick to her stomach.
Billy noticed how this made her feel and spoke up,
“Mrs. Lesnett, they cannot hang me if I am not there, can they…?”
Billy watched and waited… and about a week later on the 27th of April, conveniently Pat Garrett headed out of town to White Oaks to collect money for Taxes. This would take a few days.
The following afternoon of April 28th 1881, Bob Ollinger was loading his 10 Gauge Whitney Shotgun with 18 buckshot in each barrel, taunting Billy as he did…
“A man that gets one of these loads will feel it,”
Olinger barked at Billy, with a taunting smile…
Kid replied,
“I expect he will, but be careful Bob, or you might shoot yourself accidentally.”
As expected at 5pm Bob and the prisoners went to dinner at Wortley’s. Billy waited a few minutes then told Bell he needed to use the privy out back.
It is possible that the escape could have started immediately after being unlocked from the chain connected to the floor. If so, then a struggle would have started inside Billy’s room leading through the hall and down the stairs. However, Bell’s corpse was found with his gun holstered. Did he have another one in his hand? Likely not if he was unlocking Billy from the floor… Let’s try again!
On the way back up the stairs from the privy, Billy’s heartbeat began to pick up pace as he trotted up ahead of his captor. Bell was trailing with a holstered pistol and likely one in hand in case Billy made a run for it. As Billy reached the top he slid the iron shackle down his large wrist and over his small hand and jumped around the corner at the top.
When Bell reached the top step Billy slapped him across the side of his head with the heavy iron shackle, fracturing his skull. Probably bleeding profusely from his head, Bell staggered around stunned. Billy tried to hold Bell, but he could not and he got loose but not before the Kid snatched the gun from his hand. Once he had it, he commanded Bell to surrender. His plan was likely to tie Bell up and slip out of town quietly.

Before we proceed, it is possible and very likely that ex-Tunstall employees, Godfrey (Gottfried) Gauss or Sam Corbett could have planted a gun for Billy in the privy, which he would have retrieved and hid in his pants and under his shirt until back inside the building where he could get it out without anyone seeing the business. Also depending on how long the chains on Billy’s wrists were he may have been unshackled temporarily by Bell to use the privy.
Either way, at the top of the steps, Billy had a gun in Bell’s face. Whether it was Bells or a planted gun we may never know. Because Billy later told a couple pals different accounts of how it went down, it would seem he was covering for someone.
On the way down Bell turned to the left to get back down the stairs putting his right hand up in hopes that Billy would not shoot. Billy shot and the ball tore through the right side of Bell’s under armpit and out his left side. He staggered down the stairs and exited the  building.
Godfrey Gauss lived with Sam Wortley in an old warehouse behind the Lincoln Courthouse and had been doing yard work that day. Gauss said he was in the rear yard of the courthouse when he heard a scuffle inside followed by a shot fired and someone running down the stairs.
Gauss:
“Deputy Bell comes out of the door toward me. He fell right into my arms and expired the same moment I laid him down dead.”
Gauss said he then ran around to the east side of the building.
“When I arrived at the garden gate leading to the street, in front of the courthouse, I saw the other deputy sheriff, Ollinger, coming out of the hotel with the other county prisoners where they had taken their dinner. I called him to come quickly. He did so, leaving his prisoners in front of the hotel.”
After Bell fell, The Kid smashed through the weak door to the armory and snatched Ollinger’s shotgun and hobbled back into his prison room where he could see the hotel where Ollinger was and waited.
Gauss:
“When Ollinger had come close up to me, and while standing not more than a couple yards apart, I told him that I was just laying Bell dead on the ground in the yard behind, and before he could reply, he was struck by a well directed shot fired from a window above us, and fell dead at my feet. I started to run for my life to reach my room and safety, when Billy the Kid called out to me”… “Don’t run, I won’t hurt you! I am alone, and master not only of the courthouse, but also of the town, for I will allow nobody to come near us. You go and saddle one of Judge Leonard’s horses and I will clear out as soon as I can have the shackles loosened from my legs.” 

Gauss:
“With a little prospecting pick I had thrown him through the window, he was working for at least an hour, and could not accomplish more than to free one leg. He came to the conclusion to wait for a better chance, tied one shackle to his waist belt, and started outside. Meanwhile I had saddled a small skittish pony belonging to Billy Burt as there was no other horse available, and had also at Billy’s request, tied a pair of bed blankets behind the saddle.” 
While Billy was struggling with his leg irons, Sam Wortley entered and helped him get at least one leg free. Afterwards, Billy raided the armory for some firepower, loading up with guns and plenty of ammo. He was then all over the house, peeking out all the windows and doors before finally coming out to the upper porch where he sat on the banisters while cheerfully whistling a tune. Local stonemason Bob Brookshire started across the street, Billy yelled for him to go back or he would kill him. Nobody dared interfere. If anyone had, surely they would have taken their last breath that day.
Billy addressed the small crowd gathered below. He told them that he was fighting for his life and didn’t want to hurt anyone.

He explained to the crowd that as he grabbed Bell’s revolver and told him to hold his hands up to surrender, that Bell decided to run, and he had to kill him. He stated that he was standing pat against the world and did not wish to hurt anybody.
Gauss remembers Billy’s exit:
“When Billy came downstairs at last, on passing the body of Bell, he said, ‘I’m sorry I had to kill you, but I couldn’t help it.” and as he passed the body of Ollinger he gave him a nudge with his boot, saying, “you are not going to round me up again!”
Gauss and Billy went out back where Gauss had the pony tied up. When Billy climbed the horse, the loose chain dangling from his leg shackle startled the horse and bucked Billy off. Billy ordered one of the Tularosa prisoners to retrieve it. He was Alexander Nunnelly and he resisted thinking he’d be held accountable. Billy assured him saying, “You can tell them I made you do it.”
After tucking the chain into his trousers, Billy mounted the horse again and yelled out to Godfrey,
“Goodbye Gauss old boy, I may never see you again! Tell Billy Burt I’ll send his horse back!”
Turning his horse he called out to the rest of the spectators,
“Don’t bother to look for me on this side of Ireland! Adios Boys!”
Gauss waved his hat at Billy as he rode off out of town to the west, into the sunset. Reports say he was singing.
Billy went to the Agua Azul area and disappeared into the Capitan mountains. Billy Burt’s horse found its way back to Lincoln. Billy went to his Pal Yginio Salazar’s family home for help getting out of the chains. Salazar later confirmed:
“Billy laid out in the hills and came to my house to eat near Las Tablas. I told him to leave this place and go to Old Mexico.”

The rest is history…or mystery!