Police believe an elderly New York man who shot and killed his daughter-in-law before escaping into the wilderness is alive and on the run three years after the murder -- and they're hunting for him in states from New York to Arizona.

Eugene Palmer, 75, escaped into a vast New York forest after he gunned down his daughter-in-law, Tammy Palmer, outside her Stony Point, N.Y. home on Sept. 24, 2012.

While family members insist the elderly Palmer died in the woods, police said Monday they suspect he is alive and possibly being assisted by others in his escape, according to local press reports.

"We have no reason to believe he's dead," Haverstraw police Detective Sgt. George Lutz told CBS 2. "As a matter of fact, we believe he’s alive."

Acting on a theory that Palmer was assisted by someone in his escape, detectives traveled to Arizona and Colorado in pursuit of him, according to a local newspaper.

"We still believe that he is very much alive and that he has been, or is being assisted by others," Haverstraw police Detective Michael Cruger told the Journal News on Friday. "We also believe that there are others who have not come forward yet that may have some information on where he is or has been."

FLASHBACK: Where is Eugene Palmer?

Palmer waited for his 39-year-old daughter-in-law to place her to two children on a school bus before shooting her three times with a bolt action shotgun as she walked up the driveway toward her home, police said. Palmer, a retired part-time park ranger, then fled into Harriman State Park -- a 46,000-acre stretch of woodland filled with caves, root cellars and abandoned mine shafts that borders the man's home, according to police.

Palmer's sons claim their father -- a severe diabetic -- died in the woods, but authorities have long suspected he escaped the park -- launched an international manhunt through Interpol to track him down.

Lutz told FoxNews.com at the time that Palmer drove to his niece's home shortly after the alleged killing and confessed to the crime. He also left money with his sister to pay his taxes and told the woman to give him an hour before contacting authorities, according to Lutz.

Hours after the shooting, police found Palmer's abandoned pickup truck on an old fire road about a quarter mile into the park. An extensive manhunt ensued, using air and foot patrols as well as bloodhounds. A "hit" was detected by one of the dogs, leading police to a campsite within the park, but it remains unclear whether the scent belonged to Palmer.

The Haverstraw Police Department also requested assistance from state and federal law enforcement, including the FBI. They found no conclusive evidence of Palmer in the park, other than his truck parked deep into the woods.

"He knows this park like the back of his hand," Lutz said in 2013 of Palmer, known to locals as a so-called "Mountain Man," well-versed in the many trails and caves inside the park.

Police say Palmer became increasingly enraged over "domestic issues" between Tammy and her estranged husband, Eugene's son, John. Tammy Palmer had reportedly filed an order of protection against her husband, meaning John could not step foot on the 3 1/2 acres of land where both Tammy and Eugene lived in homes close to each another.

The family, meanwhile, has claimed Palmer acted out of character and snapped that morning, suggesting the alleged murder was not planned in advance. They told local media outlets Palmer fled the scene in his slippers, leaving his breakfast uneaten on his kitchen table.

Lutz appeared skeptical of such claims, telling FoxNews.com in 2013, "I don't know how you'd know what somebody was wearing unless you were actually looking at them."

"He waited for his grandchildren to get on the bus before executing their mother," he said. "That's pretty cold-blooded."

In 2014, a judge awarded the value of Palmer's estate – estimated at $2 million in property – to his grandchildren as compensation for their mother's death. 

FoxNews.com's Cristina Corbin contributed to this report.