Two more suspects were also arrested in the case, said Mississippi public safety spokesman Warren Strain. They are 21-year-old Douglas McPhail and 19-year-old Anquanette L. Alexander. Both have been charged with obstruction of justice. Seven people have now been arrested in this case.
Officers Benjamin Deen, 34, and Liquori Tate, 24, were making a traffic stop in the evening, when they were shot. They were taken to a hospital, but did not survive.
Suspects allegedly fled the crime scene, stealing a police cruiser and using it as a getaway car.
The gun was recently found, when a maintenance crew was mowing grass along city streets came across a plastic bag containing a gun, Strain said. The gun was found along one of the routes investigators believe the suspects had taken, when they fled.
The state's crime lab branch in Biloxi carried out ballistics tests, confirming the gun as the murder weapon.
Within hours of the shooting, four suspects were in custody.
Joanie Calloway, 22, was charged with two counts of capital murder, the Mississippi Bureau of Investigation said Sunday.
Marvin Banks, 29, also faces two counts of capital murder, along with counts of grand theft auto and felon in possession of a firearm. Police charged his brother, Curtis Banks, with two counts of accessory after the fact of capital murder, the agency said. And a fourth suspect, Cornelius Clark, was charged with obstruction of justice Sunday, the mayor's office said.
Another suspect, Abram Wade "Pete" Franklin, 29, was arrested Wednesday and charged with obstruction in the case, Mississippi Bureau of Investigation spokesman Warren Strain said.