The gunman behind a deadly shooting at Brown University in December appeared to have been aggrieved by personal failures and sought retribution against those he deemed responsible, federal authorities said on Wednesday.

More than four months after Claudio Manuel Neves Valente opened fire on the Ivy League campus, killing two students and injuring nine others, officials with the FBI’s Boston division announced they had concluded a significant portion of their investigation into the shooter.

Neves Valente, a 48-year-old Portuguese national, also killed a Massachusetts Institute of Technology professor, Nuno Loureiro, in a separate shooting at his home outside Boston on 15 December, authorities said. Neves Valente was found dead from a self-inflicted gunshot wound on 18 December at a New Hampshire storage facility following a manhunt.

Neves Valente confessed to the attacks in a series of videos and audio recordings made after the shootings, authorities say. He did not express remorse.

Authorities said on Wednesday that Neves Valente was “committed to conducting the attack” on Brown University, which he began to plan in 2022. The FBI said the gunman lacked family or friends, who could have seen warning signs and alerted law enforcement.

The FBI said it determined he acted alone and his victims were “symbolic in nature”, saying Brown University and Loureiro represented to Neves Valente “his personal failures and injustices he perceived were inflicted by others over time”.

Neves Valente attended Brown two decades ago after completing a physics program at Instituto Superior Tecnico in Portugal, which he attended with Loureiro. He withdrew from Brown in 2001 and left the United States.

He later obtained lawful permanent residency in the US in 2017 while living in Florida. He was unemployed when the shootings occurred, and the FBI said his “inflated sense of self contributed to interpersonal conflicts in his life and led him to believe he was being treated unjustly”.

The agency said it believed that as his failures outweighed his successes, Neves Valente’s “paranoia increased, compounding his continued inability to thrive, leading to him being mentally unwell and committed to dying”.