In the refined language of the law, it's called a plea bargain. But more often than not, say defense attorneys, it's a deal with the devil.

The latest example is playing out in Atlantic County Court, where a jury is deliberating the fate of Craig Arno following testimony by Jessica Kisby, his former girlfriend and alleged accomplice in the Taj Mahal carjacking-murder case.

Both were arrested in May 2010 in the murder of Martin Caballero, a North Jersey grocer who traveled to Atlantic City to celebrate his daughter's birthday on the night of May 21 and ended up dead.

Caballero was carjacked from the casino's garage and driven to a rural area in nearby Hamilton Township where he was brutally stabbed, then dumped on a dirt road. His cherished Lincoln SUV was set afire.

Kisby, 26, offered the horrific chronology from the witness stand, putting the knife in Arno's hands.

Her participation in the case against Arno was part of her deal with the Atlantic County Prosecutor's Office. In exchange, she will spend 30 years in prison with no chance of parole.

Not a great deal, but better than life, which is what 46-year-old Arno faces if he is found guilty of murder. The jury will enter its third day of deliberations on Tuesday.

On the stand, Kisby was required to tell the truth, as defined by the prosecution. Nothing more.

She gave her account in chilling fashion, at times giggling and playing with her ponytail, at other times sounding almost cavalier.

In closing arguments on Thursday, Eric Shenkus, the public defender who is representing Arno, described Kisby as callous and smug.

First Assistant County Prosecutor James McClain went one better. She is a "coldhearted, cold-blooded murderer," he told the jury.

"You saw who she was" when she testified, McClain said. "It was not a pretty sight."

Under Kisby's deal, an arrangement that is standard in state and federal courts, it doesn't matter.

The prosecution doesn't care if the jurors like Kisby, only that they believe her.

And if they don't buy her version of what happened? No worries for Kisby. Her deal stands.

By definition, plea deals involve unsavory characters with much to gain. In 2001, Philadelphia mob boss Ralph Natale got a 13-year sentence on racketeering and murder charges after testifying against wiseguy "Skinny Joey" Merlino.

Natale implicated Merlino and several codefendants in a series of gangland hits. The jury failed to convict Merlino and his associates for any of those crimes, though it did find them guilty of other charges.

Natale still got his deal.

In 2003, hit man Len Jenoff got 23 years in prison in return for his testimony against Cherry Hill Rabbi Fred Neulander, who had hired Jenoff to murder his wife. Jenoff was not particularly happy with the trade - he said he was privately promised less time - but he made out better than the rabbi, who is doing life.

Jenoff testified twice. The first trial ended in a hung jury. It didn't matter for him.

"All the cooperating witness is required to do is testify truthfully," said veteran defense attorney Richard Sparaco, of Cherry Hill. "The outcome is not relevant."

Prosecutors don't want cooperating witnesses to feel they have to exaggerate or bolster their testimony to convince a jury, Sparaco said.

"There shouldn't be any incentive to lie," he said.

That's the reason the deal a cooperator strikes is not contingent on the verdict.

Conversely, as a defense attorney who has cross-examined witnesses who have cut deals, Sparaco said he always looks for ways to suggest that the witness is an opportunist who is only saying what he believes the prosecution wants to hear.

"You want to . . . raise questions about their credibility," he said.

Natale and Jenoff learned how much time they would spend in prison at their sentencing hearings. Kisby already knows what she will get.

"She's no saint," McClain said in his closing argument, adding, "she will spend more time in prison than she's been alive."

Kisby has maintained that Arno committed the murder. But Arno, who took the stand in his own defense, said that it was Kisby who killed Caballero and that she came to him for help in disposing of the victim's car. It was he said, she said - and the jurors have to decide who told the truth.

Shenkus has called the plea bargain prosecutors have struck with Kisby a "deal with the devil." But from her perspective, it wasn't much of a bargain.

Kisby will be four months shy of her 55th birthday when she walks out of jail in 2040.

Contact George Anastasia

at 856-779-3846 or ganastasia@phillynews.com.