JOHNSTOWN, Colo. -- Two teenagers accused of beating a 7-year-old girl to death while playing a game of "Mortal Kombat" have been arrested and charged as adults in the case.

Police said the victim was the step-sister of one of the suspects.

Lamar Roberts, 17, of Westminster, Colo., and Heather Maria Trujillo, 16, were taken into custody Tuesday night.

According to the arrest affidavit, Roberts and Trujillo were baby-sitting Zoe Garcia at her home when Trujillo and Garcia were wrestling as they always do, karate kicking, punching and kicking.

Read The Arrest Affidavit

However, court records said a witness saw Roberts kicking and body slamming her. The witness said Roberts didn't know how bad he was hitting Garcia because he was drunk.

When Garcia lost consciousness, Roberts and Trujillo tried to wake her up by placing her in a bathtub, the affidavit said. They also cracked open an egg and put it in her mouth to make sure Garcia was not "messing with them."

The teens waited for 15 minutes before contacting police because they were afraid "the cops were going to get mad" because teens were watching a child, the affidavit said.

When Johnstown police arrived, they found Garcia unconscious and not breathing at her home.

Garcia died from her injuries at North Colorado Medical Center.

Garcia's mother, Dana Trujillo, told 7NEWS, "she was a good student, she loved school, and she was a good girl."

"She was my sidekick, I took her with me everywhere." Trujillo said.

The teens face one count each of felony child abuse resulting in death.

"We are talking about a pair disciplining a kid, but when a kid is harmed in this kind of violent situation, we are going to take it very seriously," said Weld County District Attorney Ken Buck.

An autopsy conducted on Garcia found she had a broken wrist, 20 bruises and bleeding under the spine and in the brain.

Two twins were inside the home as well. Police said they were removed and are now in the custody of protective services.