The body of the younger Arum, an experienced mountain climber, was spotted Friday afternoon from a National Park Service helicopter at about the 7,700-foot level on the north face of 8,500-foot Storm King Mountain, park spokeswoman Kerry Olson said.
Previous flights had been made in this area, but recent snow melt made it possible to locate the 49-year-old Seattle environmental attorney's body, she said.
It wasn't possible to retrieve the body, but Olson said it was clear to searchers that Arum was dead.
"There was no doubt of that," she said, adding it appeared that Arum had fallen.
National Park Service workers were trying to develop a plan to recover the body, which is in an area so difficult "that people can't rappel down or climb up to it," Olson said.
The search began Monday after Arum failed to return from a solo weekend trip to scale the mountain, which is about 85 miles northeast of Seattle. Family members said the climb was part of Arum's goal of reaching the summit of the 100 highest peaks in the state.
"His plan was to climb Storm King on Saturday, Aug. 28, so it's probably a safe assumption that he fell that day," Olson said.
Arum's backpack was found Wednesday on a trail on the mountain's less arduous south side, Olson said. The backpack was found at about 7,400-feet along a climbing route, and climbing gear was missing from the pack.
Climbers often take only essential gear to lighten their load while attempting a summit.
Arum's smaller pack was found higher on the mountain on Thursday, and Olson said his body was found about 300 feet below that spot in an extremely steep area with a lot of loose rock.
About 20 people, some using trained search dogs, participated in Friday's search, along with four helicopters, two of them King County sheriff's aircraft with heat-seeking equipment. Counting coordinators and support workers, about 50 people were involved in the search, Olson said.
John Arum's profile on the website of his Seattle law firm, Ziontz, Chestnut, Varnell, Berley and Slonim says he served on the board of the Washington Environmental Council from 1997-2004 and from 2006 until the present.
He got his undergraduate degree in political science from Reed College in Oregon and graduated from the University of Washington Law School.
Other lawyers in his firm did not immediately respond to Associated Press e-mails seeking comment Friday night.
Earlier this week, Bob Arum left Los Angeles to join park rangers coordinating the search effort. He had been on a three-city tour promoting the Nov. 13 fight between Manny Pacquiao and Antonio Margarito at Cowboys Stadium in Arlington, Texas. His stepson, Todd duBoef, took over the tour that also stopped in New York and Dallas.
Representatives of Bob Arum were not immediately available for commentlate Friday night.
AP Sports Writer Dave Skretta in New York contributed to this report.