Forty years ago, Gene Mares of Richland flew 23 missions in a fighter jet with his best friend Jerry Zimmer, dropping bombs on Vietnam's jungles.

This past spring, Mares, 65, went back into those jungles to look for his fallen comrade.

Zimmer, a Marine Corps captain and F-4 Phantom II pilot, was shot down Aug. 29, 1969, in Quang Nam Province, outside of Da Nang, South Vietnam. Neither his body nor that of his crew mate, 1st Lt. Al Graf, were recovered.

But thanks to Mares' efforts, the case of Zimmer and Graf is being reopened by the Joint POW/MIA Accounting Command, an arm of the Defense Department tasked with bringing home prisoners of war and recovering the remains of service members who were lost in foreign conflicts.

"We're hopefully optimistic," said Mares, who served two tours in Vietnam. "We did this not only for Jerry, but Jerry and Al — two fellow Marines that haven't been returned to their next of kin."

Mares and Zimmer were best friends, both having come from the town of Maine, N.Y. Mares was best man at Zimmer's wedding and was godfather to his son, Craig.

They both chose the Marines, went to Vietnam and were assigned to the same squadron, Mares about six months ahead of his friend.

Zimmer was the pilot, and Mares was the radar intercept officer, responsible for the weapons system, navigation and communication. While they were deployed together, it was like being home again, Mares said.

But Mares' tour had already ended and he was stateside when Zimmer was shot down. On that fateful mission, Zimmer and Graf were supposed to prep the ground ahead of a reconnaissance team that would be going out to look for enemy activity.

According to a report declassified in 2007, the recon team arrived at the crash site a few hours later. They didn't find any parachutes and determined that Zimmer and Graf were likely consumed in the crash, with the aircraft sliding about 1,000 feet and going over a cliff.

Mares had almost considered Zimmer to be invincible, he said.

"But you're young, and you've got your own family, and you've got to go back to work too," Mares said. "And so you put it behind you and go on."

The memory of Zimmer encouraged Mares to pursue a career with the Marines. He achieved the rank of lieutenant colonel before retiring and going to work at Hanford for 12 years.

In 1970, Zimmer's widow, Elaine, remarried Ron Davis, a Marine helicopter pilot who also flew missions in Vietnam and later went to work for the FBI. They had another son and now live in San Diego near Elaine and Jerry's son, Craig Zimmer.

They began to think about Zimmer's fate when Craig grew up and started asking questions about his father, and when Elaine and Ron became empty-nesters, Mares said.

From 2001 to January of this year, the Davises networked with military sources, discovered the declassified recon report, worked with an American researcher in Vietnam to gather information about the crash and made two trips to Vietnam to try to locate the site.

In March, Elaine Davis planned a trip back and recruited Mares. He had been hesitant because it didn't seem likely they would find anything and he still harbored hard feelings toward the Vietnamese.

But his wife, Sylvia, convinced him to go, pointing out it wouldn't be any easier for him if he waited to go five or 10 years later.

On March 23, Elaine Davis and Mares were in the village near the crash site when they set out with their American contact and three villagers. They had to make their way up 1,000 feet above the village, starting out on farming trails that led past fields, grave sites and watering holes. But then the path grew steep, following a ridge around the mountain.

About a quarter of the way into the climb, Davis couldn't go on, so she and the other American turned back. Mares pushed on with the villagers, with whom he could only pantomime to communicate.

As they got to where they could see a plateau, the villagers used hand gestures and sound effects to indicate ka-boom, slide, boom, meaning Zimmer's plane had come down over there.

When Mares asked them how it happened, they pantomimed shooting a large machine gun and made a rapid-fire sound like, "ba-ba-ba-bop, ba-ba-ba-bop."

He realized it wasn't the "tat-tat-tat-tat" sound of an AK-47. To make sure, he pantomimed shooting a rifle. They shook their heads no, and one of them squatted down as if in a turret, looked up into the air and made the rapid-fire sound again.

"I was kind of wondering, 'Well, did he ever shoot at me?' " Mares said.

A little farther, the villagers indicated they were at their destination — a large hole, about the size of a swimming pool, where they performed a Buddhist ceremony to reclaim Zimmer's spirit.

They found a few pieces of material and debris, of which five were later positively identified as being part of an F-4 aircraft. That was enough to get JPAC to reopen the case, because only one F-4 was reported shot down in that vicinity during the Vietnam War.

Last month, JPAC sent an investigative team to the area that visited the crash site. A review board will consider the team's report and decide whether to attempt a recovery of remains.

Mares said he never stopped missing his friend, for whom a stone monument stands in the MIA section of Arlington National Cemetery.

"He's just a loss to this country that you really don't appreciate until later on," Mares said. "He was just another young man at the time, but when you weigh the scale, he could've been a general officer in the Marine Corps, no doubt.

"He's a friend. He's not forgotten."