Officer Brian Jackson

Across the force, Dallas police officers are grieving for one of their own after he was killed in a gunfight early Sunday morning.

Police said Officer Brian Jackson, 28, was shot under the arm in the 2400 block of North Henderson Avenue in East Dallas after he chased a gunman on foot who had reportedly threatened his ex-girlfriend and fired a shot in her home.

A homeowner said Juan Lizcano, 29, hid in his front yard on the 2400 block of Madera Street and then fired on the officer when he came through the front gate.

Two officers attempted CPR on Jackson, but by the time doctors at Baylor Medical Center had a chance to try and save his life, Jackson was already gone.

He had been married just two months when he gave his life wearing the badge he earned five years ago.

As police continue to investigate further into the shooting, many of them also mourn the loss of their fellow officer. It was the first on-duty police fatality in Dallas since 2001, and the first on Chief David Kunkle's watch.

"He was a very kind, compassionate man who cared very deeply about his wife, his family and his job," Kunkle said.

A candle-lit vigil is being arranged to help fellow officers come to terms with the loss. Jackson had gone to the crime scene to help his colleagues, just 15 minutes before his shift was due to end.

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Fellow officers try to hold back tears as they talk about Brian Jackson.

Lizcano was arrested for the shooting, along with a friend, Jose Fernandez, who police found in Lizcano's car.

However, Fernandez is no longer in Dallas police custody after investigators questioned and released him.

Fernandez said he and Lizcano went out Saturday evening to a nightclub off Interstate 35 near Manana Drive.

There, he said Lizcano became drunk and later pulled out a gun in his truck and said he was going to kill his ex-girlfriend.

He was with Lizcano when he said the suspect drove to his ex-girlfriend's home.

"He was jealous," Fernandez said. "He believed the woman was with another guy."

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Juan Lizcano sits in the back of a patrol car after he allegedly fatally shot Officer Brian Jackson.

Fernandez said he tried to stop Lizcano from going inside the woman's house, but he wouldn't listen.

"I stayed in the truck, and then the police arrived," he said. "And they got me out of the truck and then I heard many gunshots."

This wasn't Lizcano's first violent run-in with the police. He was first booked in September for threatening to kill his ex-girlfriend with a knife. Six days later, he posed again for a mug shot for a charge of driving while intoxicated.

Finally, his latest mug shot was for the murder of Jackson.

Lizcano's friends said he was typically a nice guy, but would become violent when he started drinking.

"I didn't think he would ever do that," said friend Joe Gallegos.

Friends of Lizcano said he had worked as a landscaper and had been in the United States for the past two years as an illegal immigrant.

Bert Lozano, Carol Cavazos and Brad Hawkins contributed to this report