A man who was fatally shot at a park in the Oakland hills on Tuesday afternoon has been identified as David Ruenzel of Oakland, East Bay Regional Park District police said Wednesday.

Police didn't disclose Ruenzel's exact age but said he was in his early 60s. In a news release, police said Ruenzel was a regular hiker at the park and described him as "an upstanding citizen."

They said they are investigating robbery as a possible motive for the crime.

Ruenzel's son in a statement said his dad was a loving father, grandfather and best friend. He also described Ruenzel as a brilliant writer and educator who touched the lives of many.

Park district police said they received a report from a witness who heard gunshots fired at about 3:45 p.m. on Tuesday in the area of the Huckleberry Botanic Regional Preserve. The park is on Skyline Boulevard, just south of Elverton Drive.

The witness then found Ruenzel suffering from gunshot wounds, Lt. Gretchen Rose said.

Oakland police and park district officers responded to the scene and found Ruenzel lying down on a trail south of a staging area, she said. Paramedics also responded to the trail and pronounced him dead at the scene, according to Rose.

Witnesses who were in the area said they heard three gunshots at the same time, Rose said.

Witnesses told police that they saw two men on the trail just before they heard the gunshots.

Police said one of the suspects is described as a man who is black or possibly of mixed race and in his late 20s or early 30s with dreadlocks, a medium complexion, high cheek bones, a narrow face, a thin build and was wearing dark clothing.

Police said the other suspect is described as a black man who is 6 feet tall, weighs about 240 pounds, is clean shaven with short hair and was wearing dark clothes and a black backpack. Witnesses described the man as being out of shape and "overly friendly," police said.

Police have released sketches of both suspects.

A ground search was made of the crime scene but no suspects were found, police said. However, officers recovered spent shell casings and a bullet near where the victim was found, Rose said.

East Bay Regional Park District Police Department said their probe into the shooting is still in its early stages and anyone with information about it should call their investigations unit at 510-690-6549 or their dispatch center at 510-881-1833.

NBC Bay Area's Cheryl Hurd contributed to this report.