Until recently, these men were at war with the Syrian government. Now, they’re manning checkpoints across the capital. They’re former fighters for Hayat Tahrir al-Sham, or H.T.S. The Islamist group, once an Al Qaeda affiliate, overthrew the government of Bashar al-Assad in early December. After 13 years of civil war, restoring security is one of the top priorities for H.T.S. The group has installed people like Basel al-Helal, a former rebel, to head the police in Damascus. The fighters turned police now control traffic and are trying to return property that was looted during the recent government overthrow. They also say their mission is to conduct raids to apprehend drug dealers, thieves and former government officials. Before ousting al-Assad, H.T.S. ran a local government in a part of northern Syria that it controlled. There, it was accused of rights abuses, including the jailing of critics. This has some people worried. They are concerned about how H.T.S. will govern now that it controls a much larger and more diverse part of the country. These H.T.S. fighters say concerns about them are misplaced.