A 22-year-old woman from Fresno, California, has been accused of killing her sister and her three-week-old niece out of "jealousy and sibling rivalry."

The woman, identified as Yarelly Solorio-Rivera, was arrested this Wednesday for the alleged murder of her 18-year-old sister, Yanelly Solorio-Rivera. Yarelly's 26-year-old boyfriend, Martin Arroyo-Morales, has also been accused of helping her with the killings.

The woman and the baby were shot dead using a Smith & Wesson 9mm handgun while they were sleeping in their house in Fresno, per a report in The Mirror.

Police released a video of a person walking from the crime scene to ascertain the identity of the killer. They managed to identify the person and arrested the couple last week. "We can now say with complete certainty that we have those responsible for this homicide in custody," said Fresno Police Chief Paco Balderrama.

Describing the crime scene, the police chief said: "The murder scene was traumatic for all officers, detective, EMS personnel, and crime scene technicians who responded to the scene."

"The crime left us all feeling perplexed and very angry, asking ourselves, who would do something like this – who would murder an 18-year-old mother and her three-week-old daughter while they slept?"

"We have the murder weapon, a Smith & Wesson 9mm handgun, and we have a motive - jealousy and sibling rivalry," he added. The police added that Yarelly confessed to the crime, but showed "no remorse whatsoever."

The incident took place in September this year, and the couple was arrested last week following an investigation.

The suspects have been charged with two counts of murder and are being held at the Fresno County Jail. They are currently being held in prison on a $2 million (£1.74 million) bail.

The detectives have asked people to come forward if they have any information in connection with the case, even though they have already made the arrests.

Crime Scene
Crime scene police line | Representational Image Photo: GETTY IMAGES / SCOTT OLSON GETTY IMAGES/SCOTT OLSON