BEIRUT >> In the early years of Syria’s revolt, he filmed protests in the streets of his rebel-held neighborhood, in the historic center of the city of Homs. He chanted for dignity and freedom with a green, white and black banner, the old version of the national flag.

When government forces besieged the old city, he grew vegetables on the roof of his family’s house; he cried over leaving tomatoes on the vine as he departed reluctantly under a cease-fire. Later, homesick, he quoted his sister’s poetry: “There is nothing warmer than your neighborhood, your country, your house.”

Even during the darkest times, he joked and even flirted with reporters around the world, briefing them on battles, lacing his text messages to them with smiley faces and flowers. “Soon,” he teased once during an online chat, “we’ll have our engagement.”

The man who called himself Abu Bilal al-Homsi was, in short, a classic hometown rebel. A media activist, he was well known to foreign journalists, an advocate for the rebels fighting against the government but also an important source of information. He used a nom de guerre to protect his relatives from reprisals, which could still come against his family if his real name were revealed now.

No foreign jihadi, he was a Syrian fighting to change his own country and defend his own neighborhood, and while he was religiously conservative, he seemed open to the outside world. So his old friends were shocked last month to learn that he had blown himself up, becoming, as the extremist Islamic State put it in its online praise, a “knight of martyrdom.”

Most confounding was his target: fellow Homs residents, just blocks from Abu Bilal’s old house. The two-bomb blast killed at least 30 people and wounded about 100. The Islamic State boasted that it had struck an “apostate crowd,” and used a slur for Alawites, the minority group that predominates in the pro-government district in Homs.

“I never thought Abu Bilal would do that,” said a friend, Jalal al-Talawy, who worked closely with him from the early protest days through the siege. “He wasn’t an extremist or a fanatic. But his whole attitude changed during the siege.”

Abu Bilal’s trajectory follows an arc common to a number of fighters and activists who started with relatively secular, nationalist rebel groups and moved first to the Islamists, and then to extremists like the Islamic State.

Some young insurgents switch their allegiance to the Islamic State out of ideological commitment, or coercion, or because it is their best or only option to secure arms, money and protection. But in the maddening environment of the siege of Homs, Talawy said, Abu Bilal’s attitudes — not to speak of his own — grew more and more sectarian.

Many besieged fighters, Talawy said, started to hate Alawites, who belong to the same sect as Syria’s president, Bashar Assad, and dominate senior security positions. “Before the revolution, we never had this feeling toward any sect,” he said. “But after what we passed through, our attitude changed. We hated the regime and those who are ‘pro’ them.”

In May 2014, when the fighters handed the old city back to the government in exchange for safe passage to insurgent areas, the friends parted ways, physically and philosophically.

“We will come back to this land, and we will liberate it with our blood and our body parts,” Abu Bilal declared in a video he made at the time. Then he headed north and east to join the Islamic State, while Talawy chose to pull back from extremism, sticking with insurgent groups opposed to Assad and to the Islamic State.

Abu Bilal, who was 28, grew up in old Homs, but his activist friends from there said they know little of his childhood, having met him during protests against Assad in 2011. Abu Bilal’s neighborhood, Bab al-Dreib, was one of the first to join in, and he was one of the first to become deeply involved, Talawy said.

Abu Bilal had big, sleepy eyes, chubby cheeks and a talent for communication. He spent hours online, briefing reporters about protests, battles and bombardments that were harder and harder for journalists to cover in person.

But as the siege wore on, conditions inside became unimaginable. Bombardments turned familiar childhood streets into lopsided hills of rubble and spaghetti tangles of rebar. Food ran so scarce that people made stews of fruit pits. Only the most senior rebel commanders had enough to eat.

Following the exploits of the Islamic State online, Abu Bilal held out hope that its commanders might be more honorable. In his messages to journalists, he started to blame Alawites for the suffering in Homs.

Abu Bilal whiled away the claustrophobic, empty hours by chatting online and by text. One contact, he said, was a wealthy Lebanese woman with a sports car, who sent pictures of herself in skimpy outfits from trips to Italy.

“Not even Haifa would dare to take these pictures!” he said, referring to a Lebanese pop diva known for her revealing outfits.

Another online contact, a Tunisian woman, proved more important. It turned out she had followed her brother, an Islamic State fighter, to Raqqa, Syria. Eventually, he asked for her hand in marriage.

But first came the difficult departure from Homs. Abu Bilal raged on Facebook at rebel leaders and international powers, and especially the United Nations officials who had helped facilitate the evacuation.

“They claim they are neutral — how neutral?” he wrote, accusing the officials of helping Assad and his government. “They are participating with the butcher to kick the people out of their lands and houses, instead of punishing the criminal regime.”

Weeks later, the Islamic State swept into much of Iraq, taking over the city of Mosul and declaring a caliphate. Abu Bilal was thrilled, and defended the group against fellow rebels who accused it of ignoring the fight against Assad to establish its state.

“Wait before you judge,” he wrote on Facebook. “They are devout, pure Muslims. They left everything for jihad.”

The next month, he appeared dejected again, watching the fireworks over pro-government areas after Assad was re-elected in a ballot that his opponents called a sham.

His posts grew more radical. In January 2015, he praised the violent attack on the Paris offices of Charlie Hebdo, a satirical newspaper, calling it a “blessed operation” that took revenge against “anyone bombing the Muslims.”

By April, Abu Bilal was a full-fledged Islamic State member. He married the Tunisian woman, a doctor who calls herself Umm Bilal — making him eligible for a $1,500 marriage bonus and other benefits from the Islamic State. They embarked on a honeymoon trip to Raqqa, the Islamic State’s capital on the Euphrates River. “I’m happy!” he told Talawy.

The next month, he was with the Islamic State when it swept into Palmyra, the desert city home to Syria’s most magnificent antiquities, some of which the group would later destroy. He waxed enthusiastic about the desert landscape. “We have all kinds of birds, ibis, deer,” he said.

He made time for an act of kindness, helping an anti-Assad, anti-Islamic State activist from Palmyra — an old friend — smooth relations with the group. The friend, Khaled al-Homsi, who also uses a nom de guerre for safety, said that bought him enough time to escape.

After his marriage, Abu Bilal communicated less with female reporters — though when he did, he still sometimes called them by poetic nicknames, like “Mother of Eyes.” But he assiduously courted his old friends from Homs, trying to recruit them to the Islamic State and offering to help them pay to be smuggled to the group’s territory.

“He was especially persistent last time,” said Bebars al-Talawy, Jalal’s brother, in hindsight, “as if he wanted me to replace him when he died.”

The last signal they got from him was cryptic. His status changed on his social media accounts. It now said, “Forgive me.”

His sister and parents, financially struggling refugees in a neighboring country, refuse to talk about him. “What do you want to write, to give advice to others not to be like him?” his sister said bitterly over the phone.

“My brother was martyred, and he was still normal,” she said. “May God accept him.”

© 2016 The New York Times Company