Arlington police said a driver with his two toddlers in the vehicle killed two people and injured several others in two multicar crashes and a shooting on Wednesday afternoon.
Police said the incident started as a hit-and-run and then escalated at a second crash scene where the driver opened fire.
Arlington police said 11 vehicles were involved in the two crashes, including the suspect's vehicle.
Investigators said the driver, identified as Thomas Lester Harper, ran into two cars on North Collins Street near Washington Street at about 1:40 p.m.
Police said he continued driving north on the wet street at a high rate of speed, slamming into seven other cars outside an apartment complex on the corner of Brown Boulevard and North Collins Street, police said.
"I just know my car was sideswiped, and then it was like a chain reaction, like a pileup-type thing," Danny Luckey said.
Harper's blue Chevrolet Tahoe rear-ended a gray pickup truck, police said. The man inside the truck was pronounced dead at the scene.
One of the drivers hit in the first crash and a witness had followed the blue Chevrolet Tahoe to try and get the vehicle's license plate.
Witnesses told police the man inside the Tahoe pulled out a gun and started shooting at the scene of the second crash.
Police said Harper allegedly shot and killed an apparent Good Samaritan who was trying to help.
"We're still trying to determine where exactly this young man came from -- if he was from one of the vehicles involved in the crash or if he was just a bystander or a witness to the crash and walked up," Sgt. Chris Cook said.
Billy Ray Vaughn said the man was shooting from the driver's seat and was "rambling -- half laughing, half yelling."
"[He] wasn't too concerned for the two little kids," Vaughn said. "Me and someone else were trying to get the kids out. [He] didn't even acknowledge us."
Jason King said one of the toddlers inside the Tahoe tried to get out of the wreckage right before the shooting began.
"She crawled out the top of the window, down by the side of the truck," he said. "She was crawling. When I ran to get her -- another lady was coming from the corner over here to try to get her -- and that's when this guy shoots."
The toddlers in the back of the Tahoe, twin brother and sister, were injured and taken to Cook Children's Hospital in Fort Worth. Their injuries were not believed to be serious.
Police said Harper is the father of the children.
Harper was taken to Arlington Memorial Hospital with non-life-threatening injuries in the custody of Arlington police and was later booked into the Arlington jail.
A driver injured in the multiple-vehicle wreck was taken by ambulance to a Fort Worth hospital with minor injuries.
A Tarrant County deputy constable who drove by the scene of the second wreck right after the crash told people to get down for cover when the man started shooting.
There are conflicting reports on how many shots were fired before Harper was taken into custody.
Witnesses said he was smiling as police took him away.
"He's the one who did it all, had two kids in the back seat, and he's the one who got out smiling, like nothing happened," King said.
Police recovered a handgun at the scene of the second crash.
Harper, 27, faces charges of murder, manslaughter and child endangerment.
NBC 5's Scott Gordon and Omar Villafranca contributed to this report.