ALBUQUERQUE: It was in early morning darkness that officers scrambled to sort out the chaos at an Albuquerque apartment complex where a couple had reportedly been attacked, the woman bleeding from a head injury and the man sporting a black eye and wearing blood-stained shorts.

The woman told officers her 10-year-old daughter was still inside apartment number 808 from which they had escaped.

What the officers didn't know was that the child was already dead, her battered and dismembered body partially wrapped in a blanket and set ablaze.

With the fire alarm blaring, they busted in the front door and searched the smoke-filled apartment for Victoria Martens. In the bathroom, the real crime began to come into focus.

Investigators took into custody the girl's mother, her boyfriend and his cousin.

The community was left struggling to understand how a blossoming elementary school student who loved swimming and gymnastics could have been the target of such violence.

Details of what New Mexico Gov. Susana Martinez and law enforcement officials described as an unspeakable crime emerged in a criminal complaint made public Thursday. Police said Victoria was injected with methamphetamine, sexually assaulted, strangled and stabbed before being dismembered.

The killing happened on the day Victoria was going to celebrate her 10th birthday.

"This homicide is the most gruesome act of evil I have ever seen in my career," Albuquerque Police Chief Gorden Eden Jr. said.

The girl's mother, 35-year-old Michelle Martens, her 31-year-old boyfriend, Fabian Gonzales, and his 31-year-old cousin, Jessica Kelley, face charges of child abuse resulting in death, kidnapping and tampering with evidence. Gonzales and Kelley also face charges of criminal sexual penetration of a minor.

Gonzales denied having involvement with Victoria's death while reporters yelled questions at him as he was led out of the police station in handcuffs late Wednesday. The girl's mother said nothing as she taken from the police station to a police cruiser and driven away.

Police said Kelley was hospitalised and will be booked after she's released. No details were disclosed about why she was hospitalised.

Bail was set at $1 million each for Martens and Gonzales at their first court appearance Thursday afternoon. The two did not speak in court, and the public defense lawyer who represented them did not comment about the allegations.

As news spread about Victoria's death, neighbours and friends built a makeshift memorial under a tree near the apartment complex, adorning it with stuffed animals and candles. Some hugged while others cried and prayed.

In the evening, dozens of people gathered for a candlelight vigil and the shrine grew.

Christie Zamora said Victoria attended her gymnastics class every Saturday and always seemed happy.

"She was incredibly social," Zamora said. "It's just so tragic."

Another shrine was erected at Petroglyph Elementary School, where Victoria had just started the new school year.

School officials said in a statement that, like the rest of the community, their hearts ache. "Victoria is in our thoughts and prayers as we hold our children just a little tighter on this sad day," the statement read.

Neighbours said Victoria's mother worked at a nearby grocery store deli and they were shocked to see a mugshot of her in an orange jail jumpsuit.

Mugshots of Martens and Gonzales released by police showed them with bruises on their faces. According to the complaint, Gonzales said his cousin hit him and Martens with an iron, prompting him to jump over the balcony and run to a neighbouring apartment for help. Martens also found her way outside.

Police initially went to the apartment complex early Wednesday after the neighbour reported the disturbance.

Victoria's mother told police she met Gonzales online about a month ago and that he drugged the girl so he could calm her down and have sex with her, the complaint said.

Gonzales has a New Mexico arrest record stretching back to 2004, including a felony child abuse charge, driving while intoxicated and resisting arrest. He pleaded no contest to a charge of child abandonment in 2015.

Kelley's record includes battery, domestic violence and drug charges.

The Albuquerque Journal reported that in one case, Kelley acted as a lookout while a woman allegedly raped another inmate at the Metropolitan Detention Center in September 2012. Kelley pleaded no contest to conspiracy to commit criminal sexual penetration and was sentenced to three years in prison minus nearly a year for time served.

Martens told police Kelley had recently got out of prison and that she allowed her to stay at the apartment.

Online court records show no criminal history in New Mexico for Martens.