The events started when Evans stopped a minivan with Ohio plates, with Paudert arriving moments later as backup, Assistant Police Chief Mike Allen said. Two men got out of the van with the assault rifles and opened fire on the officers, Shelton said.
"In what was probably only a few minutes, Officer Evans was shoved to the ground and the men in the minivan started shooting at both officers," Allen said. Investigators believe the van then sped away, Allen said.
Paudert, the son of West Memphis' police chief, died at the scene and Evans died at a hospital, authorities said.
Although the officers were assigned to a drug unit, it wasn't known Friday whether it was a drug-related traffic stop. Authorities declined to say why Evans stopped the minivan or what was found inside.
Traffic stopped as authorities searched vehicles on I-40 looking for the suspects, who were spotted about 90 minutes later in the parking lot of a nearby Walmart, officials said.
Dozens of officers swarmed the vehicle after a wildlife officer rammed the minivan with his car, and both suspects were shot and killed, authorities said.
During that shootout, Crittenden County Sheriff Dick Busby was shot in the arm and his chief deputy, W.A. Wren, was shot in the abdomen, authorities said. Both were in serious condition Friday morning, a spokeswoman at the Regional Medical Center in Memphis said.
The two suspects haven't been identified. Arkansas State Police spokesman Bill Sadler declined to say whether investigators knew anything about the men, but said authorities don't believe others were involved in the shooting.
The shootout occurred not far from the Walmart, and Sadler said it was fortunate others weren't hurt.
"With this many people present, somebody was watching over them," Sadler said.
Johnna Long said she was inside the Walmart with her 14-year-old son when she hear some loud pops and people screaming. She said she had received a call a few minutes earlier about a police shooting, and made the connection.
"I couldn't see what was going on," Long said, adding that she and other shoppers were confused because no one knew if the shootings would move inside the store.
Stacy Gilchrist said the scene on I-40 was "chaos." She said she saw a police officer lying in the road when she pulled up.
"It was a disaster, cars were just going everywhere," Gilchrist told Memphis television station WMC.
Hours later at the Walmart, an unmarked, blue police car was parked near the white minivan. The car's doors were open, with blood on the bumper and the asphalt below and bullet holes in the windshield.
Outside the West Memphis Police Department station, officers went in and out, some hugging each other as they passed.
Shelton said the two slain officers were doing the "most dangerous job" in the department because they dealt with drug traffickers.
"They were both very friendly, outgoing, dependable people, and I was proud to call them friends," he said.
Arkansas Gov. Mike Beebe said the killings were a reminder of the risks police face.
"I have reached out to express my condolences to the entire West Memphis Police Department, including Sergeant Paudert's father, Chief Bob Paudert," Beebe said in a statement. "This is a loss shared by all Arkansans."