Dateline: A complete investigation overview of the Brittani Marcell case, explored

When Dateline NBC aired "The Match" (featuring Brittani Marcell) on September 7, 2018, viewers were glued to their screens.

This case started with a brutal attack, went cold for years, and was later cracked by a drop of blood and a memory. Hosted by Andrea Canning, the episode dissected the near-fatal assault of 17-year-old Brittani Marcell.

So read the play-by-play of the investigation and how Brittani Marcell's attacker was pinned down after years of relentless searching.

What happened to Brittani Marcell?

It was September 11, 2008, in Albuquerque, New Mexico. Diane Marcell had unlocked her front door to meet her daughter, Brittani, for lunch. Instead, her teenage daughter lay on the floor, bloodied and motionless, while a man loomed over her, clutching a shovel.

Then the intruder grabbed a butcher knife and told Diane,

"You're next."

Diane fled and called 911 as she screamed for help. Brittani was airlifted to the University of New Mexico Hospital with severe brain trauma, skull fractures, and broken bones. Doctors weren't sure she'd survive. But Brittani fought her way back. Still, she had no memory of her attacker.

And the only clue police had was a single drop of blood left behind when the attacker escaped through a broken window.

The Brittani Marcell cold case and how it came to be

Detective Jason Morales and his team ruled out burglary as nothing was missing. Yet every lead fizzled. DNA testing hit a wall. The blood drop didn't match anyone in the database. For years, the Marcell family's hope faded.

Then Assistant District Attorney David Waymire indicted the DNA profile itself ( of an unnamed suspect) to stop the statute of limitations from expiring. This gamble preserved the case until he could fill in the missing piece.

Five years later, in 2013, Albuquerque detective Jodi Gonterman took over the cold case. She suspected Brittani's memory loss was trauma suppression.

She arranged for hypnosis therapy, and it worked.

Out of the brain fog, Justin Hansen's name emerged!

Brittani remembered him from her teen years. He was a friend's older boyfriend who hung around her mall job. Around the same time, a high-tech DNA program called Parabon Snapshot produced a computer-generated image of the suspect. The face it generated looked like Hansen's.

Gonterman visited Hansen at home, and He was friendly. But that was only until she asked for a DNA sample. He refused. So detectives went undercover to collect his DNA from a discarded fast-food cup, and got a perfect match to the blood drop at the crime scene.

The DNA test changed Brittani Marcell's case

When the DNA results came in, Gonterman said she "jumped up screaming." Hansen was arrested while shopping with his kids.

But Hansen had no prior criminal record. His fingerprints weren't found on the shovel or knife used to attack Brittani Marcell. And due to a clerical error, most of the original evidence had been destroyed before the trial.

Prosecutors believed the blood evidence was enough. Facing up to 50 years in prison, Hansen struck a no-contest plea deal to attempted murder and aggravated burglary. He never admitted guilt, but Brittani finally got closure.

Hansen told 20/20: