BOSTON (AP) — The individual identified by authorities as the shooter responsible for the tragic deaths of two Brown University students and an MIT professor had meticulously planned the attack for at least six semesters. This information was revealed in documents released Tuesday by the U.S. Department of Justice.

Claudio Neves Valente, 48, a former Brown student from Portugal, was discovered deceased in a New Hampshire storage facility shortly after he fatally shot two students and injured nine others on December 13. He later murdered MIT professor Nuno F.G. Loureiro in his home located in the Boston suburb of Brookline.

According to Justice Department officials, an electronic device containing a series of chilling video confessions by Neves Valente was recovered during the search of the storage facility where his body was found. In these recordings, he admitted in Portuguese that he had been planning the Brown University shooting for a long time. However, he did not disclose any specific motive for targeting Brown or the MIT professor, who was a former classmate from decades ago in Portugal.

Throughout the recordings, Neves Valente maintained a refusal to apologize for his actions, stating, I’m not going to apologize because during my lifetime, no one sincerely apologized to me. He further expressed a sense of resignation about his fate, claiming his only objective was to leave more or less on his own terms. He also laments his eye injury sustained during the shootings.

He described the execution of the murders as a little incompetent, but rationalized that at least something was done. Neves Valente mentioned that he had rented the storage space where his body was discovered for approximately three years, highlighting a long-term contemplation of his actions.