JACKSONVILLE, Fla. -

Michael Yacob was found guilty Thursday afternoon of first-degree murder and armed robbery in the death of a teenage convenience store clerk in 2008.

Moussa Maida was working at his family's store in Arlington on May 4, 2008, when he was shot to death.

While police had good surveillance video of the crime, the robber was wearing a mask and could not be identified. But police said the gunman cut himself at the scene.

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Nearly two years after the slaying, DNA from the blood left behind led investigators to Yacob, who was already serving a sentence in Florida prison on a conviction of aggravated assault and other charges from an altercation in November 2008 at a different convenience store.

"We're very happy with today's verdict. They spoke highly of the victim," prosecutor Bernie de la Rionda said of the jury. "This was a hard-working person trying to make a living. This defendant extinguished his life for no reason other than he wanted money."

After opening statements at Yacob's first-degree murder trial on Tuesday, prosecutors presented the DNA evidence, then showed the surveillance video taken that night.

The robber ordered Maida to put money in a bag, then to get down on the floor. But when the gunman left with the money, Maida got up to activate a button to lock the robber out. That's when the gunman fired two shots through the glass, killing Maida.

"He points the weapon through the glass ... actually pointing in the victim's direction, and discharges a second time," Jacksonville Sheriff's Office Detective Alan Leavens testified.

Maida's family stepped out of the courtroom while the video was shown, but Yacob's family remained.

Maida, 19, had recently moved to the U.S. from Syria and was trying to save money to go to college.

Prosecutors have said they will seek the death penalty. A sentencing hearing for Yacob is set for Oct. 18.