Fifteen years ago, Robert Fisher's wife and two young children were killed inside their Scottsdale home, which was subsequently set ablaze.
Fisher is considered to be the prime suspect and has been on the run ever since. He's listed on the FBI's "Ten Most Wanted Fugitives."
Despite speculation Fisher is dead, FBI agents say they believe he is alive.
"Until we know otherwise, we have to assume so," said FBI Special Agent Robert Caldwell said. "We have not found a body."
Fisher will turn 55 next week. The last known photo of Fisher is from 1999.
The FBI hopes someone will recognize Fisher wherever he is and contact authorities right away. A reward up to $100,000 is being offered.
Officials say they've had a lot of mistaken identity tips because Fisher is average in appearance.
"It's a difficult case to work because he is a loner and loner are difficult to find but you know we are going to pursue all our avenues until we do find him," Caldwell said.
Investigators hope they will solve the case because someone recognizes a distinct trait, like his puffed-out chest as he walks or his gold crown tooth.
"Fisher is an outdoorsman and is skilled in hunting and fishing. He is described as controlling, and if in a relationship will likely be the one making all the decisions. Fisher could be surviving in the wild or be your next door neighbor" FBI Acting Special Agent in Charge Justin Tolomeo said.
Fisher is believed to possess several weapons, including a high-powered rifle, and should be considered armed and dangerous, the FBI said. He does have ties to Florida and New Mexico.
Last year, the Scottsdale police said the case remains a top priority at the department.
"I think what he did to his family, what he did to his own children is such a horrific thing for people to see what happened. What he did to them is such a heinous and such a cruel thing that justice needs to be served," said Sgt. Hugh Lockerby.