The search for Pat Gregory’s killer has yielded no firm leads or suspects, authorities said, but they expressed confidence their investigation will ultimately result in an arrest.

Mr. Gregory was robbed and fatally shot a year ago while on the Iron Canyon Trail near Red Bluff, Calif., about 130 miles north of Sacramento. He had been hiking with a longtime friend, who was wounded but survived.

The investigation has now spread across the country, with the Federal Bureau of Investigation looking for similar cases elsewhere. The working theory is that the gunman was probably passing through the area, which is close to Interstate 5, a major freeway that extends from Canada to the Mexican border.

“All the planets had to be aligned for this guy to act the way he did, and not be detected,” Tehama County Sheriff Dave Hencratt said in a recent interview. The recreation area is popular with residents, located just off Highway 36E and fewer than five miles from the sheriff’s department.

“I do believe this guy is going to pop up again in another jurisdiction,” the sheriff said.

A police hotline, reward and sketch of the suspect — pictured with a light beard and wearing a cap — have attracted tips, but not the volume that would suggest a local suspect. Still, sheriff’s investigators are chasing down tips whenever they get them.

“We got one last week, looked at it today and so far it hasn’t panned out for us…,” said Sheriff’s Det. Jeff Garrett on Tuesday. “Were just waiting for that good tip we can run with.”

Detective Garrett was one of the first to respond to the trail a year ago, and has remained in contact with Mr. Gregory’s friend and hiking companion. “He’s getting back on with his life,” he said.