Eight months pregnant, Tammy Lynn Baker died from the blast of a pipe bomb rigged outside her Louisa apartment by a boyfriend who didn't want to pay child support. The killer was sentenced to life in prison.

Hiding in a closet after his parents were shot to death at their Tazewell County home, 14-year-old Bobby Hopewell suffered the same fate. The killer was sentenced to life in prison.

Serving time in a maximum-security prison in Lee County, Robert Sandoval was strangled by his cellmate after the two criminals bickered over one eating the other's breakfast. But this time, the killer was sentenced to death.

A jury's decision last week to condemn Carlos Caro for the prison killing of Sandoval marked the first time federal prosecutors in the Western District of Virginia obtained a death sentence since Congress reinstated capital punishment for some federal crimes nearly two decades ago.

But as illustrated by their earlier attempts -- the cases of Baker, Hopewell and several others in the district all ended with life sentences -- the formula for death is full of variables.

"This shows just how arbitrary the death penalty is," said Elisabeth Semel, director of the Death Penalty Clinic at the University of California-Berkeley's law school.

Each trial has nuances that only the judge or jury can fully appreciate, Semel stressed. Yet when the killing of an inmate is punished more harshly than that of a pregnant woman or a family of three, "these are the kinds of differences that people find very difficult to understand."

While most capital cases are tried in state courts, Congress has given federal prosecutors more and more latitude over the years to seek death sentences.

At least in theory, the U.S. government takes a more uniform approach to capital punishment than state courts, where the difference between life and death can depend on the zeal of a particular prosecutor, the philosophical bent of a locality's jury pool or simply whether the crime was committed in one of the 37 states that allow the ultimate penalty.

Every potential federal death penalty case must pass through a central gatekeeper.

Long before the defendant goes to trial, federal prosecutors present a detailed summary of the case to a Department of Justice review committee. The panel forwards a recommendation to the U.S. attorney general, who makes the final call.

In the Western District of Virginia -- the Roanoke-based federal jurisdiction that stretches from Winchester to Lynchburg to the most western tip of the state -- prosecutors have received authorization from the attorney general to pursue the death sentence in eight cases involving 13 defendants, according to the Federal Death Penalty Resource Counsel Project.

Only five reached the point where a jury was asked to impose a death sentence. In addition to the cases of Baker and Hopewell, federal juries also decided to spare the lives of a man convicted of killing two college students in Harrisonburg and two drug dealers who shot and stabbed a rival to death in Charlottesville.

In Caro's case, it took the jury just 2½ hours to settle on a death sentence Tuesday after hearing evidence for three weeks in U.S. District Court in Abingdon.

U.S. Attorney John Brownlee said the individual facts of each case make it difficult to draw comparisons.

"My overall perspective is that I trust juries," he said. "Those are the people we bring our cases to. So I am reluctant to ever go back and question their judgment in any case."

As for the argument that death sentences are handed down in an arbitrary way, Brownlee said: "Jurors are not asked to evaluate these things in the whole. They are asked to evaluate these things in the context of a certain set of facts that are presented to them."

One thing that made Caro's case different from the others was his past record of violence -- and the risk he continued to pose inside the federal prison system.

After receiving a long prison sentence in 2001 for drug dealing, Caro joined a gang, participated in a brutal fight on a prison yard and stabbed a rival 29 times at the Lee County prison. Despite being placed under tighter security after each offense, Caro wound up killing his cellmate on Dec. 17, 2003.

Brownlee said that with a life sentence, "he would be emboldened to continue to kill."

And unlike some of the other federal cases that resulted in life sentences, the evidence of Caro's guilt was overwhelming. Not only was a hardened criminal found locked in the same cell with a dead man, but Caro made a full confession. He said he strangled Sandoval with a wet bath towel because the inmate disrespected him during an argument that started when Caro ate his breakfast.

Caro showed no remorse and even taunted guards immediately after the killing by asking when he would get a new cell, the jury was told.

"This case was something like shooting fish in a barrel," said David Bruck, director of the Virginia Capital Case Clearinghouse, a resource for death penalty defense attorneys affiliated with the law school of Washington and Lee University.

And while Sandoval was arguably the least innocent of victims in the five death cases considered by Western Virginia juries, "it seems to me that when you have a prison killing by someone who is already serving a life sentence, the government has an argument that really resonates with the jury when they say, 'Look, we tried that and it didn't work,' " said Roanoke defense attorney Chris Kowalczuk.

Two years ago, Kowalczuk represented a man sentenced to life in federal prison for killing two James Madison University students. He agreed that when the debate shifts from an individual case inside the courtroom to the broader court of public opinion, the disparities are hard to reconcile.

"That's part of what's wrong with the death penalty," he said. "It's so all over the map."