Matthew Lee Johnson, 36, is accused of setting a store clerk on fire during a robbery. (Credit: Garland PD)

DALLAS (CBSDFW.COM) – Dallas County District Attorney Craig Watkins will seek the death penalty against a man indicted for killing a 76-year-old convenience store clerk by setting her on fire during a robbery last month.

Matthew Lee Johnson, 36, is charged with capital murder and is currently jailed on a $2 million bond.

Investigators say he robbed a Fina gas station in Garland on May 20 and doused Nancy Harris, 76, with gasoline. He set her ablaze and fled. He was caught hours later attempting to break into a home near the gas station.

Harris suffered burns on 40 percent of her body. She clung to life for five days after the attack, but died from her injuries.

At the time of the attack, Garland Police Department spokesman Joe Harn said Harris would’ve died at the scene had passing officers not noticed a quick flash of light and stopped to investigate.

They put out the fire with an extinguisher and Harris was able to describe her attacker in detail.

Johnson was picked up nearby for burglarizing a home and matched her description. Police then charged him with attempted capital murder and upgraded that charge when Harris died.

Johnson was indicted on June 21. On Monday, the District Attorney’s Office announced it would seek the death penalty during the trial.