CARACAS, Venezuela — Armando Cañizales left his viola at home that day.

Eighteen and talented, he was a success story of Venezuela’s state-run music program for the poor. But he decided it was time to join the street protests against the government that had supported his career.

As teenagers throwing rocks retreated from a line of soldiers, Mr. Cañizales moved forward alone. He said nothing as he advanced, arms outstretched, palms facing up.

Then the fatal shots rang out.

“When he fell, I didn’t even know it was him,” said William Hernández, 19, a friend and fellow musician a short distance from Mr. Cañizales during the protests last month. He never expected Mr. Cañizales, who had expressed no political views to him, to be at the march. The viola had seemed to be the only thing on his mind.

Venezuela’s political unrest is testing the loyalties of many who have benefited from the socialist-oriented government — and at times were its strongest defenders. Doctors and nurses at public hospitals hold marches to demand supplies for empty clinics. Police officers, themselves suffering shortages of food, now question the government’s battle with protesters.