FOUNTAIN, Colo. (CBS4) – The man authorities believe murdered two teenagers in El Paso County was arrested last month for domestic violence and now authorities are looking for another person of interest.

The arrest affidavit says Gustavo Marquez, 19, was arrested on Feb. 24 for forcing his child’s mother into his car, grabbing her by the throat, slamming her against the car and trying to break her fingers.

Marquez was on bond for that incident when deputies say he murdered Natalie Partida, 16, and Derek Greer, 15.

Derek Benjamin Greer, 15, and Natalie Partida, 16 (credit: El Paso County Sheriff’s Office)

Greer’s mother, Heather Ferguson, says she is devastated.

“I don’t understand what any kid could have done, or any person for that matter, to have deserved their life to be gone forever and not get to live a future.”

The El Paso County Sheriff’s Office said Marquez was taken into custody Sunday evening in connection with the double homicide.

Authorities are now looking for Diego Carlos Chacon, 18, who goes by the name Casper. Authorities believe he has information that will help with the investigation in the case.

Chacon is described as being 5-foot-9, 150 pounds with black hair and brown eyes.

Greer and Partida were reportedly best friends from Colorado Springs, and both students at Coronado High School.

On March 12, a passerby discovered their bodies in Fountain near Pikes Peak International Raceway off Old Pueblo Road.

“Deputies arrived on scene and confirmed that a male and female were lying on the shoulder of the road deceased,” the sheriff’s office said in a statement.

According to the sheriff’s office, Marquez was arrested on the charges of first-degree murder, kidnapping, aggravated robbery, and child abuse resulting in death.

Marquez remains in custody at the Criminal Justice Center in Colorado Springs without bond.

The El Paso County Sheriff’s Office investigates the deaths of two teens near Fountain (credit: CBS)

It’s not clear if anybody else was involved in the murders.

Deputies are still investigating that portion of the crime, according to Jackie Kirby with the El Paso Sheriff’s Office, “Until we are sure that we have everybody in custody who is responsible on this — we are not going to rest and our detectives have been working non-stop around the clock.”

According to Colorado court records, Fountain police arrested Marquez in a separate case on Feb. 24 on suspicion of kidnapping, assault and child abuse. Documents state that Marquez allegedly tried to force the mother of his child into his car, grabbed her by the throat and tried to break her fingers.

In that case, Marquez was granted $5,000 bond three days later on Feb. 27. Court records indicate he posted bond the same day.

Investigators will not say what led them to Marquez, his motive or how the teens were killed. They say that they have received tips in this case.

Additional Information from The El Paso County Sheriff’s Office

Anyone with information regarding this case can call the Sheriff’s Office Tip Line at 719-520-6666 or 719-520-7777.

LINK: Excerpt From Marquez’s Arrest Affidavit