Cláudio Valente is suspected of killing physicist Nuno Loureiro and two other people at Brown University, in the United States.
Authorities found Cláudio Valente dead in a warehouse in New Hampshire on Thursday night.
The autopsy determined that Valente, a Portuguese man who lived in the US, died on Tuesday, the same day that his compatriot, Massachusetts Institute of Technology (MIT) professor Nuno Loureiro, died in a hospital, the office of New Hampshire Attorney General John Formella said in a statement.
Authorities believe that, after killing two students and injuring nine others last Saturday at Brown, Valente shot Loureiro in his Boston-area home on Monday night.
Valente was a monitor at the Instituto Superior Técnico (IST), in Lisbon, where he was a coursemate of Loureiro in the 1990s, and the institution terminated his contract the year he went to study in the United States.
In February 2000, Técnico terminated the contract it had with Cláudio Neves Valente as monitor, as stated in an order published in March of that year in the Diário da República.