Joshua Gibson kills his daughter's mother, Danielle Marshall

In the quiet bedroom town of Powder Springs in the US state of Georgia, police were confronted with a nightmarish murder. Danielle Marshall, 23, was shot in her home while her nine-month-old daughter Eva was inside.

Rescue workers found Danielle on the kitchen floor “in the fetal position,” said Amy Randolph, a former Powder Springs Police Department investigator. The real murders of AtlantaAirs Saturdays at 9pm ET/PT on oxygen.

“The child had apparently been wandering around the house the whole time the mother was lying in the pool of blood,” Randolph said in the episode “Death in Powder Springs.” “It was horrible.”

Officers arrived at the home where Danielle lived with her mother, Gloria Marshall, at approximately 1:15 a.m. on January 14, 2013, after receiving a 911 call from Joshua Gibson, Danielle's ex-boyfriend and Eva's father.

Gibson told the 911 dispatcher he was outside the house and could hear Eva crying inside. He said he tried to call Danielle, but she didn't come out or answer the door. Powder Springs Police officers were sent to the house to conduct a wellness check, which led to the grisly discovery.

In a police interview, Gibson, who lived with his current girlfriend, said that he and his girlfriend were sleeping at home at the time.

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Investigators found that Gibson was still having sex with his ex Danielle. “Gloria [Danielle’s mother] “I was working at night,” Randolph said, “and Joshua came over.”

Officials took note of the potentially explosive love triangle. “To say that Danielle's relationship with Joshua was complex would be an understatement,” said Jesse Evans, a former prosecutor in the Cobb County District Attorney's Office, The real murders of Atlanta.

“At this point, Joshua allowed us access to his cell phone and handed over his clothing for further forensic examination,” Evans added.

Danielle Marshall's past with Joshua Gibson

Investigators discovered that Danielle became pregnant shortly after she began dating Gibson. “It happened so fast,” said her friend Pamela. “They went through the roof like a rocket.”

Gloria, Danielle's mother, had reservations about Gibson. “The guy had control issues,” said Gloria The real murders of Atlanta.

Danielle was happy about her motherhood, but Gibson reacted differently. “It was too hard for him,” Pamela said on the show.

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A year-old Cobb County police report revealed that there was animosity between Danielle and Gibson's girlfriend, who nearly ran Danielle over with her car.

When Gibson's girlfriend was questioned by police about Danielle's murder, “she said that Danielle was not a threat to her,” Randolph said, “and that she had not done anything to her.”

Gibson's girlfriend claimed she was at work until 9:30 p.m. the night Danielle was killed and then went home with Gibson after 11 p.m. Gibson later went to check on Danielle. Investigators obtained a search warrant for the girlfriend's cellphone to confirm her alibi.

According to Evans, the girlfriend's alibi was confirmed by cell phone records. Gibson's phone records seemed to confirm his story that he had texted Danielle several times and called her before going over to her house.

While investigators tried to move the investigation forward, Danielle's family members had to cope with the terrible loss. Her mother, Gloria, could not bear to live in their house.

“I went straight to the spot where she had died,” said the grieving mother. “I knelt down and told her I was sorry. I kissed the floor in the kitchen where her body had been and said goodbye.”

Investigators change direction, then the case is closed

Investigators turned their attention to Jeremy Pitts, another man Danielle was dating. During a police interview, Pitts said he was with Danielle the night of the murder.

But Pitts changed his story. He later told them that he had been with Danielle the day before. He explained that he had actually been at a party with a group of friends the night she was killed.

According to investigators, this alibi was confirmed by other party guests. “We looked at Jeremy's cell phone and cell phone records and were able to conclusively determine that he was not at the crime scene when the murder was committed,” Evans said.

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Pitts has been ruled out as a suspect. “At this point we are trying to go through [Danilelle’s] “We called and went over the schedule again,” Randolph said. “At some point we ran out of phone numbers.”

At the end of 2013, the case was no longer being investigated. Hoping for a break in the investigation, Danielle's mother “waited and waited and waited,” she said. “Time is the devil.”

Danielle Marshall's case reassigned

A year after the murder was committed, the investigation was turned over to the District Attorney's Office's cold case team, led by Nick O'Conor, a former investigator with the Cobb County District Attorney's Office.

He began by thoroughly analyzing the phone records of Gibson and his girlfriend. He found a number that both phones had in common and a call at 11:22 p.m. when the couple said they were sleeping.

The call came from a high school friend of Gibson's who still lived in the area. The man was not identified during the initial investigation.

Through information from a cell phone tower, investigators learned that the man was very close to Danielle's house at the known time of the murder, O'Conor said.

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Investigators paid Gibson's friend “a surprise visit at his workplace,” Cadwell said.

“He denied from the beginning that he knew anything about or had anything to do with Danielle's death,” O'Conor said. But the witness eventually broke down.

“He comes out and admits that he went to Danielle's house with Josh the night Danielle was murdered,” O'Conor said.

According to the investigator, the boyfriend said Gibson mentioned the possibility of a threesome with Danielle and drove her to Danielle's house.

The man said he noticed that Danielle was not expecting them. She was very uncomfortable, O'Conor said. The real murders of AtlantaThe witness added that he and Gibson returned to his car and that Gibson went back into the house for a few minutes.

“That information broke the case,” O'Conor said. Investigators believed Gibson's friend when he said he had not seen a gun or heard a shot.

To learn more about the case, watch the episode “Death in Powder Springs” The real murders of AtlantaAirs Saturdays at 9pm ET/PT on Oxygen.