Grieving families speak out as police hunt for killer of 2 Colorado teens

— -- As authorities in Colorado hunt for the killer of two teenagers who were found dead on the side of a road, their families are left grieving.

Derek Benjamin Greer, 15, and Natalie Partida, 16, were found dead Sunday morning, their bodies lying on the shoulder of a road 15 miles from their high school in Colorado Springs, the El Paso County Sheriff's Office said.

Natalie's cousin, Hannah Ortega, told "Good Morning America" that Natalie and Derek "went everywhere together."

"They loved each other," Ortega said. Derek was Natalie's "truest friend," she said.

"They had a whole life to live," she continued. "They don't get to have kids, they don't get to graduate high school, they don't get to work their dream jobs, they don't get to live anymore. Nobody deserves to get their life taken."

Natalie's grandmother, Margaret Partida, told "GMA" that "[Natalie] meant the world to us. Natalie was a girl full of just joy and happiness. She always had a smile on her face."

Partida, overcome with emotion, recalled the last words her granddaughter said to her.

"She had a couple of tears in her eyes, and she said, 'Grandma, I want to tell you how much I love you,'" Partida said. "I never dreamed that would be the last I would see of my granddaughter."

Partida said she has no idea who committed the crime.

"It ended so quickly," Partida said. "They were just beginning life."

Derek's mother, Heather Ferguson, told "GMA" she wanted to speak out because "he wasn't just somebody's garbage. He deserves to be remembered and deserves to have justice."

She described Derek as "so loving."

"He was my best friend and loved me so much," she said.

Derek's stepfather, Jeff Ferguson, said Derek was always talking and usually the center of attention.

"He made an impression on people," he said.

He added, "We just hope that at some point the person or persons who did this realize how many lives they destroyed."

"A part of you is gone, forever," Heather Ferguson said. "Our home will never be the same."

While the sheriff's office ruled the deaths as homicides, authorities have not released how the teens were killed, saying they are waiting until the toxicology reports come back.

As police look for the killer, Jacqueline Kirby, spokesperson for the El Paso County Sheriff's Office, said authorities are "aggressively pursuing all leads."

The sheriff's office asks anyone who "sees anything out of the ordinary for their area" to call the sheriff's office at 719-390-5555.