A year ago, Ibrahim Qobani was an idealistic 19-year-old revolutionary who sang about freedom.

Always dressed in a scarf and fingerless gloves woven with the colors of the Syrian rebel flag, Qobani worked with a team of pro-democracy activists in Syria's northern Idlib province. He would sing from the rooftops during boisterous anti-government protests, complete with humorous animations that begged the international community to help stop Syrian government atrocities.

But today, Qobani appears much different in a series of YouTube videos.

Gone is the scarf with colors of the rebel flag. Instead of leading the chants, the young man stands in the crowd smiling as one man sings, "We destroyed America with a civilian plane, turned the World Trade Center into a pile of dirt. If you call me a terrorist, I say it's an honor."

In another video, Qobani stands cheering with a crowd of bearded men as a little boy sings, "Our commander is Bin Laden. He showed the Americans the strength of our faith." A man gives the boy a knife, which he proceeds to slice through the air as he sings, "Our police is Nusra. Just wait Alawites. We will come to slaughter you."

It was a chilling warning to the minority religious sect of Syrian President Bashar al-Assad, who has stacked the top ranks of his security forces with fellow Alawites.

Qobani declined several requests to speak with CNN. Several of his friends, however, confirmed that he is now a member of Jabhat al-Nusra, or the Nusra Front, the most famous of the hard-line Islamist rebel groups now fighting against the Syrian regime.

Qobani's ideological evolution is symbolic of a broader shift that many Syrians say they're seeing nearly two years after the anti-government uprising began.

"There is an increasing militarization and now increased radicalization of the revolution," said Rafif Jouejati. She is the English spokeswoman for the Local Coordination Committees in Syria, one of the first groups to organize peaceful anti-government protests in the spring of 2011.

"Jabhat al-Nusra continues to make gains," Jouejati said. "They continue to increase in popularity, particularly as they begin to implement social services."