With a third victim gunned down along a northern Colorado road this week, authorities are looking into whether a serial shooter is behind the random string of violence over the past two months.
Cops say there's one essential element in cracking these types of cases: the public.
"The public is absolutely critical in a case like this," said NBC News law enforcement analyst Jim Cavanaugh. "All these cases are broken by some help from the public."
It was the help of a witness in Kansas City, Missouri, last year who told police she had been followed by another driver and then jotted down his license plate. That driver ended up being the alleged suspect in at least 12 shootings that terrorized three Kansas City-area highways.
Law enforcement in a rural area north of Denver are hunting for the shooter or shooters responsible now that two of the three known attacks in the area ended in fatalities. The latest occurred Wednesday night, when 65-year-old William Connole was found dead on a sidewalk near his home in Loveland, a community of 71,000.
"Channel what might be fear into being productive," Loveland Police Chief Luke Hecker asked residents during a news conference Thursday. "Help us look, keep your eyes open, pay attention and look for things in your neighborhoods that may be out of place."
FBI officials who are assisting in the investigation have stopped short of calling the shootings a "sniper" attack. Officials also haven't said whether there is any ballistic evidence in common between the shootings.
The first known shooting occurred April 22, when driver Cori Romero, 20, was struck in the neck while driving through the nearby town of Windsor. Romero survived.
Then, on May 29, 48-year-old John Jacoby was shot and killed while riding his bike in Windsor. Police said there was no relationship connection between Jacoby or Romero.
There is also no relationship tying those cases with Connole — although Windsor and Loveland are about 15 miles apart. "There is no positive link ... but we have not been able to rule out a link either," David Moore, Larimer County Sheriff's Office spokesman, told reporters Thursday.
Police also looked into reports of shattered car windows, but found no evidence that they were caused by shootings and were likely the result of road debris in some cases, said Larimer County Sheriff Justin Smith.
Connole, a grandfather of five, was known to take walks at night to help him fall asleep. That is what he was doing Wednesday when he was shot before 11 p.m. local time, family told NBC affiliate KUSA.
Granddaughter Sadie Rogers, 15, said his death has left the family "numb." They remembered him for looking out for everyone in the family, even when he was suffering from cancer.
"He just did everything for everyone he could," she added.
If the three cases are the work of a serial shooter, he or she likely has no connection to the victims or any particular target, said Eric Hickey, dean of the California School of Forensic Studies who has studied serial killers.
The victims are "proxies for his anger and whatever he's angry about," he said, speaking generally.
"He'll make mistakes," Hickey said. "They always do."