In the final chapter of the novel, Bruno sneaks underneath the massive fence surrounding the Auschwitz concentration camp in an attempt to help Shmuel find his father and is herded into a gas chamber, where he dies alongside his best friend. Bruno resolves to help his friend Shmuel find his father and views the opportunity as their final adventure together before he travels back to Berlin with his family. Shmuel is able to acquire a prison uniform resembling striped pajamas for Bruno to wear and lifts the fence so he can crawl underneath.

Once Bruno enters the camp, they begin their investigation, and he witnesses the horrors of the concentration camp for the first time. After searching in vain for an hour and a half, Bruno and Shmuel do not find his father but are herded into a large group by Nazi officers and instructed to march to the gas chambers, which resemble spacious showers. The innocent boys are too young and naive to recognize that they are in serious danger and share a tender moment just before the poisonous gas is released into the chamber. Once the chamber door is slammed shut and chaos ensues, Bruno holds onto Shmuel's hand tight and does not let go. The boys die clutching onto each other for comfort, and their friendship endures through the horrific experience.

In The Boy in the Striped Pajamas, Bruno and Shmuel die together in the gas chambers of Auschwitz. Bruno, the son of the camp commandant, is still too young and too naive to understand what goes on here, and still thinks of his interactions with Shmuel as all of a bit of a game.

Nonetheless, Bruno has developed a close friendship with Shmuel and wants to do whatever he can to help him look for his father. Although Bruno still doesn't comprehend what Auschwitz is and what it stands for, he does at least understand why Shmuel would want to find his father. Tragically, Bruno's fateful decision to help eventually leads to his death in the gas chamber.

Having resolved to help his best friend, Bruno digs his way under the fence that separates the grounds of the family home from the concentration camp. He brings with him a spare set of pajamas, which makes him look like a prisoner when he puts them on. Because of this, Bruno is mistaken for a prisoner by the camp guards and herded along with Shmuel and other prisoners into a gas chamber. There the two friends perish together, holding on to one another right to the end.

Bruno is a nine-year-old boy from whose perspective The Boy in the Striped Pajamas by John Boyne is told. The story starts in Berlin, but Bruno's father is a Commandant in the Nazi army and gets promoted by Hitler himself. This promotion comes with a new assignment: the commandant of the concentration (death) camp called Auschwitz. Bruno is naive and tells the story just as he sees and experiences it.

Bruno is out exploring one day and discovers another little boy sitting morosely on the other side of the fence. His name is Schmuel and he is exactly the same age as Bruno; they even share the same birthday. Their relationship continues over time, but eventually Bruno is going to be moving back to Berlin with his sister and mother and he wants to play at least one time on the same side of the fence with his best (and only) friend, Schmuel.

Schmuel has been unable to find his father (we deduce that his father has been exterminated), so Bruno agrees to come inside and help his friend look for clues. Schmuel brings Bruno a uniform (which Bruno refers to as "striped pajamas"), and Bruno fits right in since his head had been shaved because of lice--though he is "fatter" because he has, of course, been eating well.

The boys discover nothing as they explore the camp, but just as Bruno is considering sneaking back under the fence and go home, some soldiers come and round the two boys and some others up and herd them into 

a long room that was surprisingly warm and must have been very securely built because no rainwas getting in anywhere. In fact, it felt completely airtight.

Bruno assumes the soldiers are just being nice and trying to keep this group from standing in the rain and catching colds. Bruno and Schmuel are glad to have each other as they wait together in the dark, neither realizing what is about to happen to them. 

The next line of the novel says this:

Nothing more was ever heard of Bruno after that.

Obviously what happened is that Bruno, Schmuel, and the others the soldiers rounded up that day were gassed to death and presumably their bodies were then burned.