Updated at 9:30 p.m. ET Saturday
Police in Kissimmee, Fla., just south of Orlando, reported late Friday that two officers there had been shot.
Officer Matthew Baxter, a three-year veteran of the department, was killed, and Sgt. Sam Howard was in "grave critical condition," Kissimmee Police Chief Jeff O'Dell told reporters early Saturday.
Later Saturday, Howard died of his injuries, the police department said in a statement on posted to Facebook.
Baxter was married to another officer and had three children. Howard is also married and a father.
Orange County Mayor Teresa Jacobs had earlier written on Twitter that both had been killed, calling the shooting a "[h]eartbreaking loss of two of Kissimmee's finest officers."
President Trump sent his condolences to the officers on Twitter.
Kissimmee Police Chief Jeff O'Dell said Saturday that 45-year-old Everett Miller was arrested several hours after the shootings, charged with first-degree murder for killing Baxter. Authorities didn't say if Miller is facing charges for Howard's death.
According to the police chief, Miller was a Marine veteran recently committed involuntarily for a mental evaluation by the Osceola County Sheriff's Office, and had threatened law enforcement on Facebook, O'Dell said.
"This is a tough time for each one of us," he told reporters early Saturday. O'Dell said the department hasn't "experienced this in over 25 years."
"At this point, I'd ask you to please keep the men and women of the Kissimmee Police Department, the families of the fallen officers, the law enforcement personnel in the central Florida area in your thoughts and prayers," he added.
The officers were shot in an area with "some drug activity," he said.
"There are no county or jurisdiction lines when it comes to our Law Enforcement Brotherhood," Osceola County Commissioner Fred Hawkins Jr. wrote in response to the shootings.
Later in the same night, two other officers were shot in a separate incident about 165 miles north, in Jacksonville, Fla.
The Jacksonville Sheriff's Office wrote that one of the officers was in critical condition and one was in stable condition in local hospitals.
Mike Bruno, the director the office's Department of Patrol and Enforcement, told reporters that four or five officers responded to an "attempted suicide call" at a home around 11 p.m. They thought it was an active shooter situation after hearing gunshots from inside.
A suspect "began shooting through the door at the officers," using a "high-powered rifle," then went outside and exchanged gunfire with the officers, Bruno said.
The suspect was shot by police and died at a hospital.
In a third separate incident, in southwestern Pennsylvania, two Pennsylvania state troopers were shot in Fairchance on Friday. The suspect in that incident was also killed.
State police say both troopers were alert and conscious after the shooting. One trooper was flown to a nearby hospital, and another was transported by ambulance.
Sources tell KDKA that one trooper was shot in the stomach and was in surgery at a hospital in Morgantown around 10:30 p.m. Sources say the other trooper was shot in the hand.
Sources say troopers were serving a warrant when the shooting broke out.