Complex sentence: Shanina's friend Anna Samsonova remembered that Roza sometimes returned from her friends in Ustyansky District to her college dormitory between 2 and 3 am when the doors were locked and the students tied several bedsheets together to help Roza climb into her room.
Split into simpler sentences: Shanina's friend Anna Samsonova remembered that Roza sometimes returned from her friends in Ustyansky District to her college dormitory between 2 and 3 am. As the doors by that time were locked the students tied several bedsheets together to help Roza climb into her room.