Jodi Arias' defense attorneys may have already punched a hole in medical examiner Dr. Kevin Horn's timeline of Travis Alexander's death during the cross examination of a prosecution witness.

GET CAUGHT UP: Jodi Arias & Travis Alexander: Killer romance?

Mesa, Arizona, police Det. Esteban Flores testified that, at some point in the investigation, he thought the gunshot to Alexander's forehead was the first injury. He said that was based on his conversations with Horn.

But Horn testified that it was likely Alexander was stabbed in the heart first, tried to defend himself, then had his throat slit, killing him. Then, Alexander was shot in the head.

READ FOR YOURSELF: Dr Horn's report from Alexander's autopsy

HLN contacted our own expert pathologist, Dr. Carol Terry, the chief medical examiner for Gwinnett County, Georgia. Terry attended Emory University's medical school and has 18 years of experience with forensic pathology. She analyzed Alexander's autopsy at HLN's request.

Terry agrees with Horn that the slashing of Alexander's throat is what killed him. But she says he was likely shot first, before any of the stab wounds were inflicted.

READ MORE: Doctor: Wounded Alexander fought back

When the defense begins presenting its case January 29, one of the witnesses will likely be a pathologist who disagrees with Horn's opinion of how Alexander died -- did the bullet to the head kill him, or was it the stab wounds?

So what is the significance of the sequencing of Alexander's injuries?

There are two reasons why this is important to Arias' defense.

A defense attorney's job is to create as much doubt about the prosecution's case as possible. If the defense can show the prosecution is unsure about its theory of Alexander's death, it may erode the jury's confidence in the prosecution's case.

The sequencing also matters because this is a death penalty case. If the prosecution can get a guilty verdict and prove that Arias was cruel and caused Alexander to suffer, she may be sentenced to death. However, if the defense can show that Alexander was shot in the head first, attorneys can argue that all of Alexander's other wounds happened after he died, and so he didn't suffer -- and that could save Arias from the death penalty.

Soon after Alexander's body was found in June 2008, Arias initially told police she was not involved in Alexander's death. She later changed her story and told investigators that she witnessed two intruders break in and kill him. She eventually admitted to killing Alexander, saying it was in self-defense.