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12-year-old Texas girl’s 1979 murder just solved, but the killer was executed in 2002

Authorities attributed the breakthrough to “M-Vac,” a DNA collection technique originally developed to identify food contamination.

The cold case slaying of a 12-year-old girl in Texas more than four decades ago was solved after authorities used an advanced DNA tool to identify her killer, authorities said Monday.

Gerald Dwight Casey, who was executed in 2002 for an unrelated capital murder case, was linked to Lesia Michell Jackson’s 1979 sexual assault and homicide with the help of a DNA technique known as “M-Vac,” the Montgomery County Sheriff’s Office said in a statement.

The technology, originally developed to identify food contamination but now used to collect DNA from porous and other difficult surfaces, was used to process samples discovered on Lesia’s clothing, the sheriff’s office said.

Lesia Michell Jackson.
Lesia Michell Jackson.Montgomery County Sheriff's Office

The sheriff’s office, north of Houston in one of Texas’ most sprawling counties, said it was the oldest cold case the department has solved.

Lesia disappeared on Sept. 7 after swimming at the lake in her subdivision with friends and relatives. Her glasses were found the next day, and an oilfield worker found her body near a pipeline on Sept. 13, the sheriff’s office said.

An autopsy found that she had been sexually assaulted, the sheriff’s office said.

The case remained cold until last year, when the new DNA technique was used to obtain samples from Lesia’s clothing, the sheriff’s office said.

A DNA profile was identified by state forensics experts and uploaded to a DNA database, the sheriff’s office said.

After the profile was identified as belonging to Casey, investigators compared the DNA obtained from Lesia’s clothing with a blood sample taken from Casey before his execution.

The comparison confirmed Casey as Lesia’s killer, the sheriff’s office said.

Casey was executed by injection on April 18, 2002, for a 1989 robbery and murder.

This story originally appeared on NBCNews.com.