Yeah, it was three cosmonauts during the Soyuz 11 mission. A valve broke open right before re-entry. The cosmonauts probably asphyxiated within 40 seconds. This all happened just above the Karman line (100km) which is what defines where space starts. The capsule finished the re-entry and landing process and they were found dead, they were still warm when the recovery team found them. After this the Soviets redesigned the Soyuz capsule, reducing the capacity to 2 people but allowing them to wear their spacesuits during re-entry and take-off.