The man responsible for killing two Brown University students and an MIT professor had been planning the attacks for several years and left behind video recordings in which he admitted to the shootings without explaining his motive, the U.S. Department of Justice said Tuesday.

The shooter, identified as Claudio Neves Valente, 48, a former Brown student and Portuguese national, was found dead in a storage facility in New Hampshire on Dec. 18. Authorities said he carried out a shooting at a Brown University engineering building on Dec. 13, killing two students and wounding nine others, before fatally shooting MIT professor Nuno F.G. Loureiro two days later at the professor’s home in Brookline, Massachusetts.

Federal investigators said they recovered an electronic device from the storage unit containing short videos recorded by Neves Valente after the attacks. In the recordings, he acknowledged planning the shootings for at least six academic semesters but offered no reason for targeting Brown University or Loureiro, whom he had known decades earlier while studying in Portugal.

In the videos, Neves Valente said he felt no remorse and denied claims circulating online that he had spoken Arabic or made religious statements during the attack. He said he did not intend to issue a manifesto and insisted he was not mentally ill.

Authorities said the victims at Brown were shot at random. The students killed were 19-year-old sophomore Ella Cook and 18-year-old freshman MukhammadAziz Umurzokov.

Neves Valente also described being confronted by a witness at Brown whose information later helped police identify him. He said he was surprised it took authorities several days to locate him.

Brown University said the tragedy continues to weigh heavily on its community as it mourns the victims and supports those injured.