A New York man who police say shot and killed his daughter-in-law before fleeing into the wilderness nearly seven years ago is being added to the FBI’s Top 10 Most Wanted list, authorities announced on Wednesday.

Eugene Palmer, of Stony Point, N.Y., is wanted in the Sept. 24, 2012, shooting death of his daughter-in-law, Tammy Palmer, in what authorities described as a cold-blooded and premeditated murder.

Authorities have long said that they believe Palmer, now 80, is alive and living under an alias. At a news conference on Wednesday, the FBI said they suspect Palmer -- considered armed and dangerous -- is hiding in upstate New York or Florida.

"In our eyes, the victim always comes first and we will never give up until justice is served," said FBI Assistant Director-in-Charge, William F. Sweeney, adding that the reward for Palmer has been increased to $100,000.

"Eugene Palmer might believe we've given up on finding him but he'd be wise to think again," Sweeney said.

On an early September morning, Palmer allegedly waited for his 39-year-old daughter-in-law to place her 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 bordered the man's home, according to police.

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, Detective Sgt. George Lutz of the Haverstraw Police Department told Fox News.

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.

"He waited for his grandchildren to get on the bus before executing their mother. That's pretty cold-blooded." — Detective Sgt. George Lutz of the Haverstraw Police Department

The Haverstraw Police Department then 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 of Palmer, known to locals as a so-called "Mountain Man," well-versed in the many trails and caves inside the park.

A law enforcement source previously told Fox News the U.S. Marshals service was assisting police in the investigation, which has taken authorities to areas across the country.

Police say Palmer became increasingly enraged over "domestic issues" between Tammy and her estranged husband, Palmer’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.

Palmer's two sons, John and Clarence, could not be reached for interviews.

The family has previously said that Palmer -- a severe diabetic -- likely died in the woods of Harriman State Park. His sons told a local newspaper that Palmer acted out of character and snapped that morning, suggesting the alleged murder was not planned in advance. They claimed Palmer fled the scene in his slippers, leaving his breakfast uneaten on his kitchen table.

"If the police didn't botch the hunt in the beginning, my father's remains would be where they belong," Clarence Palmer told the Journal News in 2013. "They were afraid of going into the woods; afraid of a man with a shotgun, supposedly. If he wanted to be found, he would have finished himself off here. He went into the woods. I think he fell into a diabetic coma."

Authorities have always been dubious of such a claim.

"I don't know how you'd know what somebody was wearing unless you were actually looking at them," Lutz said. "He waited for his grandchildren to get on the bus before executing their mother. That's pretty cold-blooded."

Sweeney, who was joined Wednesday by Rockland County authorities, described Palmer as 5-foot-10 with brown eyes and gray hair and noted that his left thumb is deformed. He said Palmer is an avid hunter and experienced outdoorsman who is also interested in cars and auto racing.

Sweeney said the FBI has a "greater than 90 percent success rate" in capturing or locating criminals when they are placed on the Top 10 Most Wanted list. Palmer is the 523 person to be added to that list.

"Not only do we have a nationwide reach but our capabilities extend far beyond our borders," Sweeney said.