Why is the pipel hanged?

Night, written by Elie Wiesel, is a story about Wiesel's own experiences during World War II and living in a concentration camp.
Wiesel describes the concentration camps and the amount of dehumanization that occurred daily. He states that violence, including hangings, occurred often. He also describes how the concentration camps kept prisoners in line. Prisoner functionaries known as "Kapos" were prisoners who were forced by the Nazi guards to supervise other prisoners of the camp. These men often selected younger boys to be their assistants. These younger boys were known as "Pipels."
In chapter four of the novel, Wiesel describes a particularly sad event. In this chapter, a pipel is hanged alongside two grown men. The boy is hanged because he helped ruin an electrical plant that was supplying energy to help hurt the prisoners; he was also possessing weapons. This particular hanging was worse for the prisoners to watch than other hangings, for a few reasons. Because of his small size and light weight, the pipel was not killed immediately and suffered a painful and slow death. It was also torturous to watch this boy die because of boy's kind nature. This child did not want to harm any of the prisoners and did not attempt to save his own life by blaming others. It was, as Wiesel writes, "not a small matter to hang a child in front of thousands of onlookers."

Night is the true story of Elie Wiesel, a Jewish man who was forced to work in German concentration camps during the Holocaust until he was freed in 1945.
Throughout his narrative Wiesel tells his readers of many horrible things he experienced and witnessed. Pipels were boys who worked as assistants to the kapos, who were also technically prisoners, but worked for the guards in concentration camps as prison supervisors. It is heavily implied that pipels were sometimes sexually exploited by the kapos they served and that they would consequentially be rewarded by those in charge.
The specific pipel that Wiesel mentions is one that was kinder than most and well-liked by other prisoners. The young boy was killed because it was discovered that the Oberkapo he served was hiding weapons, and the pipel refused to give up any possible information about what the Oberkapo was doing, even after being tortured.