A massive backlog in DNA testing at the FBI crime lab put a Kirkland doctor and his family in grave danger.

The central criminal figure in all this is a retired Seattle cop- turned-convicted- bank-robber named Gary Krueger. We've been reporting this week that a special cold-case task force considers Krueger a prime suspect in at least three unsolved murder, including the 2001 stabbing death of Bellevue realtor, Mike Emert.

Now Investigative Reporter Chris Halsne has confirmed if not for errors by both the FBI and Bureau of Prisons, Emert's accused killer would likely have been locked up years ago. And that would have prevented Dr. Craig McCallister from getting beat in the head with a gun during a violent attempted home invasion in March of last year.

“That light was on, so you could kind of see this gun in his hand and he kind of turned toward me like that and I thought, ‘OK. Here it comes,’” said McCallister.

McCallister told KIRO Team 7 Investigators as he arrived home after dark, a pair of "burglars" demanded he let them inside, where his wife and teenage daughter were watching TV. He fought with everything he had, and the men eventually fled. The unknown motive for the crime ranges from scary to terrifying.

PART 1: Former SPD Cop Suspected Hit Man

PART 2: FBI Delay Makes Widow's 'Blood Boil'

PART 3: Possible Hit Man Cop Named In '81 Murder Of Retired Officer

PART 4: FBI Backlog Could Have Cost Kirkland Doctor His Life

PART 5: DNA Match Made Too Late Because Of Feet-Dragging By Feds

PDF: Police Confirm DNA Match in Realtor Murder: See Proof Here

SLIDESHOW: Suspect, Murder Victims, Crime Scenes

TIMELINE: Slow Road To DNA Match

“To think that two guys in there 60s, dressed like they’re ready for war, just meandered down the street that night is a little bit difficult to swallow,” said McCallister.

Especially since one of the criminals turned out to be a former Seattle cop - and well-known convicted felon- named Gary Krueger.

A multi-jurisdictional cold case homicide task force is looking at Krueger as the prime suspect in a series of unsolved murders that might include contracted professional "hits.”

Dr. McCallister has been watching KIRO's investigations this week with great interest.

“We feel very lucky. I feel incredibly fortunate to be alive today, knowing how close I came to a man who apparently has a history or murder,” said McCallister.

Kreuger is no longer a threat because he drowned in Lake Washington after fleeing the McCallister house. However, our investigation discovered that he should never have been in the McCallister's driveway in the first place.

According an FBI email and a King County Sheriff's Department memo, 3-1/2 years before the Dr. McCallister assault, a DNA sample from Gary Krueger was sent to the FBI testing center in Quantico.

It sat and sat, crushed under a backlog of some 300,000 cases. It turns out, if they'd run the DNA right away they would have known it matched one collected in 2001 from the brutal murder scene of Realtor Mike Emert in nearby Woodinville.

“It doesn’t surprise me that samples fall through the cracks and that guys like Gary Krueger are walking around out there as cold cases waiting to be solved,” said McCallister.

That second armed robber that came to the McCallister home is still at large. Detectives think John Bradshaw is probably dead, but if he's not, they believe he'd know invaluable information about his partner Gary Krueger. If you've seen Bradshaw since March of 2010, call police immediately.