HARD YEAR. STEPHANIE GOSK, NBC NEWS. >>> IN DALLAS ONE OF THEIR OFFICERS WERE FOUND SHOT TO DEATH IN HIS SQUAD CAR AND THAT HE WAS EXECUTED. THE SUSPECT LATER KILLED OF A HIGH-SPEED CHASE, AND MORGAN CHESKY WITH THE INVESTIGATION TONIGHT. >> Reporter: JUST OUTSIDE DALLAS THIS IS WHERE A GUNMAN'S RUN FROM POLICE ENDED AFTER HE FATALLY SHOT OFFICER DARRON BURKS INSIDE HIS PATROL CAR OVERNIGHT THEN OPENED FIRE ON OTHERS. >> I KNOW THE WORD AMBUSH HAS BEEN THROWN AROUND IN THE LAST 24 HOURS OR SO, THAT'S NOT WHAT HAPPENED HERE. OFFICER BURKS WAS EXECUTED. >> Reporter: INVESTIGATORS SAY IT BEGAN NEARLY 30 MILES AWAY IN A SOUTH DALLAS NEIGHBORHOOD WHERE NEIGHBORS REPORTED A FLURRY OF GUNFIRE. POLICE ARRIVED TO FIND ONE OFFICER WOUNDED AND A SUSPECT WHO KEPT SHOOTING. THE SHOOTER WOUNDED TWO OFFICERS THEN SPED AWAY LAUNCHING A MASSIVE CHASE. POLICE NOW IDENTIFYING THE GUNMAN AS COREY COBB-BEY. >> COBB-BEY APPROACHED OFFICER BURKS AND TALKED WITH HIM BRIEFLY THROUGH THE DRIVER'S SIDE WINDOW AS HE RECORDED THE ENCOUNTER WITH A CELL PHONE. THE SUSPECT THEN PULLED OUT A HANDGUN AND EXECUTED OFFICER BURKS AS HE SAT IN HIS VEHICLE. >> Reporter: THE SHOOTING COMING EIGHT YEARS AFTER ANOTHER GUNMAN AMBUSHED DPD KILLING FIVE OFFICERS AND WOUNDING NINE OTHERS. >> BUT DESPITE OUR HURT, DESPITE OUR