A California woman killed her younger sister and 3-week-old daughter over "jealousy" and a "sibling rivalry," authorities said. 

Yarelly Solorio-Rivera, 22, was arrested Wednesday in connection with the Sept. 24 shooting death of her 18-year-old sister, Yanelly Solorio-Rivera, and her baby Celine. Yarelly's boyfriend, Martin Arroyo-Morales, 26, a gang member, was also arrested, police said.

Both are charged with two counts of pre-meditated murder, Fresno Police Chief Paco Balderrama said Thursday.

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California sibling killing

Yarelly Solorio-Rivera, 22, has been arrested in connection to the murders of her sister, Yanelly Solorio-Rivera, and her 3-week-old baby Celine. Fresno, California authorities said the killing stemmed from "jealously and sibling rivalry." (Fresno Police Department)

"We have the murder weapon, a Smith & Wesson 9mm handgun, and we have a motive — jealousy and sibling rivalry," he said. "We saw no remorse whatever, no guilt."

Officers were called at about 7:20 a.m. on the day of the killings to a home over reports of multiple gunshots heard within a bedroom in the house, Fox San Francisco reported.

Balderrama said "the scene was traumatic for all officers, detectives, EMS personnel, and crime scene technicians who responded to the scene."

Fresno baby killing

Yanelly Solorio-Rivera, 18, and her 3-week-old infant daughter, Celine Solorio-Rivera, were killed in September. Yanelly's older sister, Yarelly Solorio-Rivera, and Martin Arroyo-Morales have been charged in the killings. (Fresno Police Department)

When they arrived, police found Yanelly Solorio-Rivera and the child dead. Solorio-Rivera was shot multiple times.

Investigators had strong suspicions early on but didn't have enough evidence to make an arrest, the chief said. 

Fresno sibling murder

Martin Arroyo-Morales, 26, has been charged in the death of his girlfriend's sister and her newborn. (Fresno Police Department)

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"This was an intricate and well-planned murder," Balderrama said.