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May 10, 2015, 4:18 AM UTC / Updated May 11, 2015, 3:49 AM UTC

Three men and a woman have been charged in the fatal shooting of two police officers during a traffic stop in the southern Mississippi city of Hattiesburg, authorities said Sunday.

The officers, Benjamin J. Deen, 34, and Liquori Tate, 25, were gunned down Saturday night after Deen pulled over a Hyundai for a speeding violation and called for back up, officials said.

Four suspects, including two brothers, were arrested in different locations after a manhunt that lasted into the early hours of Sunday morning.

Marvin Banks, 29, was charged with two counts of capital murder, and counts of grand theft auto and being a felon in possession of a firearm. Joanie Calloway, 22, was charged with two counts of capital murder, while Curtis Banks, 26, was charged with accessory after the fact of capital murder.

Cornelius Clark was arrested later and faces obstruction charges, Hattiesburg Mayor Johnny DuPree told NBC News. Clark, 28, was allegedly a passenger in the vehicle at the time of the shooting.

Officer Benjamin Deen, left, and Officer Liquori Tate. Hattiesburg Police Department via AP

The suspects fled, with Marvin Banks alleged to have escaped in one of the officers' vehicles, said Warren Strain, a spokesman for the Mississippi Department of Public Safety.

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DuPree said during a news conference Sunday that the shooting occurred after Tate arrived to provide backup for Deen, who was first on the scene. Other details about how the shooting incident unfolded remained vague Sunday.

"We're piecing all that together at this point. There's still a good bit of investigating to do — there are several pieces of the puzzle that we need to bring together to bring clarity to what has happened here," Strain said.

The Mississippi Bureau of Investigation has taken control of the investigation, DuPree said.

Deen and Tate were the first Hattiesburg cops to die in the line of duty in three decades. Deen was a K9 handler, while Tate had been on the force for less than a year.

DuPree said the loss of Tate, who had an "infectious smile" and Deen, who was a married father of two, was "a tragedy for all Americans."

Tate's mother, Yolanda Ross, told NBC station WDAM of Laurel that the last words her son spoke to here were "I love you, too, Mama."

"It's not an easy thing to deal with," Ross said. "He was a wonderful son. A mother couldn't ask for anyone better."

DuPree told MSNBC's Alex Witt on Sunday afternoon that he still couldn't speculate on the motive of the suspects.

"I wish we could get into the head of people who do these kind of things," DuPree said. "It was a traffic stop, and something happened to make the officer believe he needed to call for backup, which he did."

Mississippi Governor Phil Bryant said in a statement that he was "mourning" the loss of the officers. "This should remind us to thank all law enforcement for their unwavering service to protect and serve," he wrote.

Curtis Banks, Joanie Calloway, Marvin Banks Hattiesburg Police Department

SOCIAL

All 3 suspects transported out of Forrest Co. to be housed until initial appearance for the death of 2 HPD officers. pic.twitter.com/5xeaBjs5CY — Ryan Moore (@RyanMooreMS) May 10, 2015

Both Hattiesburg Police Officers have died. Terrible. Prayers to the entire community and families. — Oxford Police Dept (@OxfordPolice) May 10, 2015

BREAKING:4th suspect charged in shooting death of 2 HPD officers Cornelius Clark charged with obstruction of justice. pic.twitter.com/hKBpWSSoAG — Ryan Moore (@RyanMooreMS) May 10, 2015

— Matthew Grimson and Elisha Fieldstadt

M. Alex Johnson of NBC News and The Associated Press contributed to this report.