FAIRFAX, Calif. -- A 67-year-old man found shot to death on a hiking trail in Northern California, still holding onto the leash of his wounded dog, was a tantra teacher who made DVDs on yoga for lovers and taught classes at a clothing-optional retreat.

Detectives are looking for three people of interest in the killing of Steve Carter. Two of them are seen on surveillance video released by investigators Tuesday evening.

Authorities say these two people, seen in an image from surveillance video, are "persons of interest" in connection with the shooting death of Steve Carter, 67, on a Marin County, California hiking trail. CBS San Francisco

The footage from a convenience store in Fairfax near the trail shows a long-haired man in a black hat and a woman with dirty-blond hair in dark clothing.

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Numerous people called authorities to report a trio of people were seen in the area acting strangely, reports CBS San Francisco. The third person of interest - a man -- was also captured in the video, but the footage was too grainy to release, reports the station.

A hiker found Carter's body Monday evening along a scenic trail about 20 miles north of San Francisco, the Marin County Sheriff's Department said. His Doberman pinscher also was shot, but it survived and was turned over to an animal welfare group, Lt. Doug Pittman said.

Carter and his wife, Lokita Carter, founded the Ecstatic Living Institute based in Middletown, a town about 100 miles north of San Francisco that was ravaged last month by one of the most destructive wildfires in California history. As a tantra teacher, Steve Carter participated in training sessions across the U.S. and in Canada and Costa Rica, the San Francisco Chronicle reported.

"He's been an amazing, gentle, loving, kind being," friend Shakti Padmin told CBS San Francisco. "His mission was to bring more love into the world, to create happy, connected, spiritual, intimate relationships."

The couple released DVDs on tantric massage, yoga for lovers and meditation. They also taught classes at Harbin Hot Springs, a clothing-optional retreat in the Middletown mountains that burned down in the wildfire, according to the newspaper.

Logan Rose, director of the Ecstatic Living Institute, said the Carters recently led retreats for couples in Costa Rica and had come back to California so Lokita Carter could receive breast cancer treatments.

"It has been a very traumatic season for us with Lokita's cancer, then the Valley Fire that destroyed our beloved Harbin Hot Springs where we offered the majority of our workshops," Rose said. "This is the most devastating blow. We are heartbroken."

Carter's brother, Michael Carter, said he knew of no one who disliked his brother.

"I can't imagine that it's anything other than a random thing," he told the Chronicle. "All of it seems very random and unbelievable. Nothing makes any sense."

Steve Carter is believed to have driven to the trail near Fairfax in his silver 2003 Volkswagen Jetta station wagon with the license plate number 6PPG662, authorities said. The car was missing, and the killer is believed to have stolen it, Lt. Pittman said.

"Persons associated with this vehicle as far we're concerned should be considered armed and dangerous," Pittman told CBS San Francisco.