Millan, 54, was stabbed in the chest during an evening run on Iron Horse Boulevard on November 20, 2014.
Police said a driver discovered Millan's body on the pavement between Phelps Lane and Rotary Park. The area is a popular spot for biking and running.
"They still talk about it," said Kathy Chamberlin, who has lived in Simsbury for 40 years.
"I'm surprised something like that could happen in this neighborhood," said Joe Orosz, who has lived in Simsbury for 50 years. "It's really not completely isolated."
"It feels like a void," said Chamberlin. "We don't hear any updates. We don't know what's going on."
Millan's murder is now under review by Connecticut's Cold Case Unit, which stepped in about four months ago.
"We start completely afresh and look at wherever the evidence takes us," said Leonard Boyle, Deputy Chief State's Attorney.
Boyle said the unit looks at all evidence with a new set of eyes.
"We're asking the lab to do some retesting of items, to test some items in perhaps some different ways."
The unit is re-examining everything - from the first calls to police to evidence to interviews.
"There will be new interviews conducted, some of people who have already been interviewed and perhaps a few folks who have yet to be interviewed," said Boyle.
Investigators are pursuing leads both in and out of state, as well as any connections to Millan's job as a high-placed executive.
"Is there any reason anyone in any way connected with her employment might have had animus toward her," said Boyle. "That's being pursued and that's continuing to be pursued as we go forward."
Boyle is urging anyone who may have seen something that night to call investigators, no matter how trivial the information might seem.
"We know that there were people on Iron Horse Boulevard around 8 p.m. on November 20, 2014 who have not come forward or have not yet been identified," said Boyle.
The Cold Case Unit is working alongside Simsbury Police, State Police, the Hartford State's Attorney and the FBI to aggressively investigate the case. There is currently a $40,000 reward being offered for information leading to an arrest.