Besides detailing a hidden aspect of the civil war, the story serves a dual purpose: to signal viewers - and his bosses - that Muir wants to get out of the office for work as much as he can.
"A huge part of this for me was a promise that I was not going to be tethered to the anchor desk," said Muir, who officially replaces Diane Sawyer on Monday night.
Muir, 40, joins NBC "Nightly News" anchor Brian Williams and Scott Pelley of the "CBS Evening News" at one of the three jobs generally considered the pinnacle of American broadcast news. Muir is also a generation younger than the 55-year-old Williams and 57-year-old Pelley.
Muir is already known well to "World News" viewers as Sawyer's chief sub, and, since the start of the year, he has anchored half as many weeknights (46) as Sawyer (92), according to news consultant Andrew Tyndall. Muir has groomed himself for the job since he was a child.
As a latchkey child of divorced parents growing up near Syracuse, Muir took comfort from the news "family" that appeared on his television each evening. He watched ABC's Peter Jennings, trying to guess who would be named "person of the week." At 12, he wrote to Syracuse anchorman Ron Curtis for advice on how to get into the business and had an internship at WTVH-TV by the next summer.
Muir became so familiar that the newsroom had a spot on the wall to mark how much he'd grown each year. When he was still at nearby Ithaca College, WTVH hired Muir to anchor the weekend news.
After five years at WTVH, he moved on to Boston and, in 2003, came to ABC News. Hurricane Katrina was one of the first places his work attracted attention.
"All of the elements of being a news anchor he does superbly," said David Westin, the ABC News president who hired Muir. He shows versatility in reporting, interviewing and working in the studio, he said.
Network anchors traveling to stories used to be more commonplace, and when Westin appointed Bob Woodruff and Elizabeth Vargas to replace Jennings a decade ago, it was on the theory that at least one would be on the road regularly. It has become less frequent, in part because of costs. Muir considers the reporting an important part of his identity and, he believes, what viewers expect of him.
"The evening news is evolving rapidly, and I think we have to be extraordinarily nimble," he said.
The dinnertime newscasts have been shadowed by predictions of their demise for about as long as Muir has been working. But each has seen its viewership increase over the past year. Muir, who frequently tweets during commercial breaks, said the programs' abilities to sum up the day's most important stories is valuable at a time people are bombarded with information.
Tyndall, whose website monitors the content of evening newscasts, said "World News" tends to be faster-paced with a higher story count when Muir is anchor. More than half of Muir's newscasts have nine or more reports with correspondents or interviews, compared to 29 percent for Sawyer. Muir resists the notion that he packs the broadcast with more material, but he said he wants to keep some things short so more important stories have room to breathe.
Muir will start "World News" with a new executive producer, Almin Karamehmedovic, who he said shares "a thirst to travel the world."
It's difficult to judge at the start where a new anchor will take a broadcast. Westin likened it to a president appointing a new Supreme Court justice - the person may not turn out as liberal or conservative as was initially thought.
Tyndall's name is mud at ABC because of a report last winter criticizing the "Disneyfication" of "World News," specifically a greater emphasis on consumer and entertainment news at the expense of global concerns.
"When I see reports like that or words like that, I think of the moment when I'm standing in Tahrir Square with a producer and photographer and Mubarak's men come charging in on their horses with their whips," Muir said. "Or when we were in Mogadishu and were fired upon by forces linked to al-Qaida."
He added, "I'd be very hard-pressed to tell them that what we're doing out there is 'soft.'"
Muir's role will be slightly different than that of his predecessor; ABC said. George Stephanopoulos will be the network's main anchor on breaking news reports. Muir said that's fine, and it ties into his desire not to always be deskbound.
He recently unearthed the letter that the Syracuse anchorman sent back to the advice-seeking 12-year-old, which today sounds prescient.
"Competition in television news is keen," Curtis wrote. "There's always room for the right person. It could be you."