AUBERVILLIERS, France — A Chinese tailor, Zhang Chaolin, emigrated to France with his wife and two sons in 2006 in search of a better life. They settled in Aubervilliers, a working-class suburb of Paris, where a decade of striving finally put that life within reach.

His sons, now in their 20s, work and have their own families. Last year, the younger son had his first child, making Mr. Zhang a grandfather.

But those dreams of stability came to an abrupt end this year under a pleasant August sun. A group of young men, barely old enough to drive, assaulted Mr. Zhang, who was 49, as he walked in Aubervilliers with two friends he had known since childhood.

Shouting racist slurs, the youths took a small bag from one of the men, and savagely beat them, leaving Mr. Zhang and his friends crumpled and bloodied on the sidewalk. The bag contained only candy and cigarettes. Mr. Zhang died five days later.