(CNN) -- Sheriff's deputies delivered the fatal wound that killed a man who, along with his wife, gunned down two police officers and a civilian in Las Vegas on Sunday, a sheriff's department official said Wednesday.
Authorities had earlier said the woman shot and killed her husband before taking her own life. But Assistant Sheriff Kevin McMahill told reporters Wednesday that a review of forensic evidence at the scene and autopsy results showed that police fatally wounded the gunman.
"We made a determination that she did not shoot him. He did suffer a gunshot wound, and we believe the entrance wound was here," McMahill said, pointing to his own collarbone.
In fact, he said, the fatal wound was delivered from a rifle fired by police. McMahill said three officers fired on the suspect.
"We do not believe any of her shots hit him," he said.
McMahill said investigators were reviewing a "tremendous" amount of graphic video of the suspects during the rampage.
"The video shows you exactly how vicious and coldblooded these murderers were," he said.
In the Walmart security video, released by police, the Millers are seen in their final moments. They are lying wounded in an aisle with various store items surrounding them -- items, police say, they used for cover. They hold firearms, which they at times point at each other. At the end of the video, Amanda Miller turns the gun on herself.
The latest developments came as still-shaken colleagues of the fallen officers wore black bands to pay tribute to Igor Soldo, 31, shot in the back of the head, and his partner, Alyn Beck, 41, struck by a bullet in the neck.
The killers apparently considered law enforcement as oppressors, authorities said. They placed a "Don't Tread on Me" flag and a Nazi swastika on one officer and left a note saying, "This is the beginning of the revolution," on the other officer's body, authorities said.
After gunning down the officers, Jerad and Amanda Miller ran to a nearby Walmart, police said, where they killed a bystander before barricading themselves inside the store during a firefight with responding officers.
On Wednesday, authorities revealed that police had previous contact with the couple on three occasions this year -- in February, April and on May 31 -- without incident. "There was no indication provided by the suspects of their anti-police feelings," McMahill said.
In February, detectives from the Southern Nevada Counter-Terrorism Center investigated threats made by Jerad Miller against the Indiana Bureau of Motor Vehicles, McMahill said. Miller threatened to shoot staff at the agency after his suspended driver's license was taken from him during a traffic stop, according to Danielle Dean, a spokeswoman for the Indiana Bureau of Motor Vehicles.
Detectives who interviewed Miller did not perceive the "potential for an ongoing threat," McMahill said.
A second contact came on April 10 when officers interviewed the Millers as witnesses in a domestic violence case, McMahill said. The couple provided voluntary statements about the alleged assault and did not display any "anti-police" sentiments, he said.
On May 31, the Millers again provided statements to police officers about an alleged sexual assault of a neighbor without incident.
"Because an individual may online espouse ideology that is anti-government or anti-police does not make them translate into a murderer," McMahill said "What happened to change these two people into murderers, we don't know."
Authorities said three weapons were recovered from the suspects: a Smith & Wesson M&P 9 mm handgun, a Ruger .38-caliber revolver and a Winchester 1300 12 gauge shotgun with a pistol grip. The weapons were not registered, as required by law.
Police officers have been kneeling in front of a makeshift memorial overflowing with flowers and miniature flags, and vowed to honor the slain officers and the uniform they deeply cherished.
"It's one thing to die in the line of duty when you're actually in the act of doing something," said Sgt. Trey Gethoefer of the Las Vegas Metropolitan Police Department. "It's a complete different feeling when your two officers are basically assassinated because of the uniform they're wearing."
The officers said they will wear their badges with pride. Las Vegas police will double up in patrol cars for the next few days as they mourn their two colleagues.
"We are the only thing that stands on that line every day between good and evil," Gethoefer said. "And we have to draw that line in the sand so the good people can enjoy the freedoms on a daily basis."
Beck and Soldo were both married with children: Beck left behind a wife and three children; Soldo, a wife and a baby.
"He had three children and a wife, he had everything to concentrate on," Gethoefer said of Beck. "When you're a beacon in your community, out of uniform and in, that speaks volumes about a person's character."
Beck walked the walk, he said. He believed in policing by foot and handshakes.
His partner, Soldo, shared the same commitment. His parents fled Bosnia-Herzegovina with their two sons in 1995 to escape a bloody war. They settled in Nebraska.
The two teenage brothers grew up to be police officers, a job they loved and cherished after the ethnic intolerance in their homeland. Their relatives are devastated to lose their son in a country they fled to for refuge.
Las Vegas residents also mourned the officers.
"When I first found out, I was so upset," said a tearful Angela Austin. The officers were a constant in her neighborhood, she said.
'I got five deaths on my shoulders'
As more details emerge, so do the signs.
Kellie Fielder said one of the suspects, Amanda Miller, was her best friend. The Millers were staying with her for about two weeks before the shooting.
She saw them leave on that fateful day, armed to the teeth.
"There were two duffel bags in a cart. They had two duffel bags on their back," Fielder said. "She just hugged me and said, 'I love you, thank you for everything.' "
She said she never thought they were planning the carnage.
"I was stupid, I guess," Fielder said. "I got five deaths on my shoulders. I should have called the cops," she said, crying. "I'm so so so sorry -- to everybody. I'm sorry."
Targeting officers at random
Police believe the couple acted alone and targeted officers at random.
The bystander who was shot was identified as shopper Joseph Wilcox, 31. He was going to confront the suspects.
"He was carrying a concealed weapon, and he immediately and heroically moved toward the position of Jerad Miller. Upon completing that action, he did not realize that Amanda Miller was with Jerad Miller," McMahill said.
Amanda Miller shot him.
Wilcox died trying to protect others.
CNN's Kyung Lah reported from Las Vegas, and Faith Karimi wrote and reported from Atlanta