On July 13, 1997, Johnson was found stabbed inside her Kill Devil Hills childhood home that had been set on fire.
The murder shook her family to the core, including sister Donnie Johnson who spoke exclusively to NewsChannel 3's Todd Corillo on Wednesday.
"Denise was a sweet girl. Happy most always. Her smile was her trademark. She just smiled all the time," explained Donnie Johnson. "We just - all of us were just devastated. We didn't know what in the world had happened"
Despite an aggressive investigation by the Kill Devil Hills Police Department, with help from the State Bureau of Investigation and the FBI, a suspect has never been identified.
"We thought it was going to be an easy thing. You know we assumed it was someone she knew. We didn't think it was random," Donnie Johnson explained.
Instead 15 years passed with each day bringing more questions than answers for the family.
"It's been hard. The non-closure of it. The 'why in the world' of it just has been hard," Donnie Johnson explained.
To help rekindle interest in the case and generate new leads, the Kill Devil Hills Police Department and Dare Community Crimeline partnered together to produce a documentary about the murder.
"I'm hoping that this documentary will encourage anybody who may know something but was too scared to come forward - to come forward. A lot happens in 15 years. Things change. People move away," Donnie Johnson explained.
She especially hopes that whoever killed her sister will also see the documentary.
"I hope the person sees it - or the people who were involved see it and it touches their heart enough that they say, 'Wow and I really just want to come clean about this,'" Donnie Johnson commented.
Donnie Johnson hopes the documentary will also be a way for people to remember Denise and her life that ended far too soon.
"She didn't ever get to get married. Never got to have children - which she loved children. Just didn't have all the beautiful things a beautiful young girl should have. Her life was taken way too short," Donnie Johnson explained.
In addition to the YouTube upload, residents of the Outer Banks can see the documentary on Gov-TV Channel 20 at 10a.m. and 10p.m. daily.