BEIRUT -- It's a happy moment, a selfie taken by a group of teenagers on a sunny day in downtown Beirut. Mohammed Shaar sits among his friends in a red hoodie and his dark-framed glasses.
The next photos, captured by journalists only moments later, are tragic. The 16-year-old lies mortally wounded, his red hoodie and his blood forming a scarlet blur on the pavement -- an anonymous civilian casualty of a car bomb that killed a prominent politician.
The before-and-after montage of Mohammed Shaar, who died of his wounds a day after Friday's bombing, has rattled Lebanese who saw in his ordinary-turned-horrifying day their own lives and potentially their own fate. The Lebanese teen has since become a symbol of a population held ransom by the country's widening violence and swelling tensions between Sunnis and Shiites, exacerbated by the war in neighboring Syria.
On Monday, hundreds of Mohammed's fellow students marched to the Starco building, outside of which the bombing happened. They held signs saying "We are all Mohammed," waved the Lebanese flag and left flowers.
The powerful car bomb targeted Mohammed Chatah, a former finance minister critical of Syria and Hezbollah. Chatah's allies in a mainly Sunni political coalition backed by the West quickly pointed the finger at the Shiite Hezbollah guerrilla group, which denied the accusations.
But the blast, on a main avenue of the ritzy downtown shopping district, killed not only Chatah and his driver, but also five passers-by -- including Mohammed Shaar.
Friends said the Shaar youth was downtown celebrating the end of the school semester, having coffee with his three friends at a Starbucks. Then they strolled through downtown to the Starco building, a complex of offices and shops. There, they took that last selfie.
Moments later, the district was shaken by the blast, which sent a plume of black smoke over the area -- and young Mohammed fell with a bleeding shrapnel wound in the head. At his funeral Sunday, sectarian anger bubbled up, with some mourners chanting anti-Shiite slogans. But more prevalent was anger over being caught in the crossfire as powerful factions -- whoever they may be -- fight out their political differences.
Mohammed Shaar, a Sunni, wasn't political or particularly religious, those who knew him said. Several hundred emerged for his funeral, and tens gathered outside, some holding signs protesting the deaths of civilians.
"Every one of us imagined ourselves in that place," activist Mohammed Estateyeh said outside the Khashakhgi mosque in the Sunni-dominated Beirut neighborhood of Qasqas after the teen's burial. "The picture of Mohammed lying on the ground -- and the picture just before the explosion -- they were four guys who were just hanging out."
Mr. Estateyeh, of the Muslim Students League in Beirut, printed black-white-and-yellow posters of Mohammed, with the Arabic-language hashtag slogan scrawled underneath: "#We--are--not--numbers." The slogan caught on online, with some people posting pictures of themselves holding it on Facebook. Montages of Mohammed's life-then-death photos circulated widely on Facebook and Twitter.
Sunni-Shiite tensions began growing after a powerful car bomb in 2005 killed the former prime minister, Rafik Hariri, who called for an end to neighboring Syria's domination of the country and criticized Syria's ally Hezbollah. Hariri's assassination was followed by more than a dozen other assassinations of anti-Syrian figures. His allies blame Syria and Hezbollah for the killings; both deny involvement.
The Sunni community's leadership is fractured. Religious hardliners preach that they are being targeted by a Shiite plot to crush them. Ordinary Sunnis, neither particularly political nor religious, complain that they feel marginalized.
Those feelings have sharply grown since Syria's uprising against President Bashar Assad began three years ago. Rebels seeking to overthrow Assad are mostly Sunni, and the most powerful are al-Qaida extremists. Syria's minorities -- including Shiites and members of the Shiite offshoot Alawite sect -- mostly support Assad or stayed neutral.
Syria's sectarian splits have enflamed Lebanon's, with its Sunnis mainly lining up behind Syria's rebels and its Shiites backing Mr. Assad. Hezbollah has dispatched its fighters to shore up Mr. Assad's forces, infuriating opponents in Lebanon.
The result has been violence rooted in Syria's war.