The suspect behind the deadly Brown University shooting and the killing of an MIT professor died by suicide days before he was found dead in a New Hampshire storage unit, authorities confirmed Friday, as investigators continue searching for a motive behind the attacks.

New Hampshire Attorney General John M. Formella said Friday the New Hampshire Department of Justice Office of the Chief Medical Examiner performed an autopsy on the body of Claudio Manuel Neves Valente, 48, who was identified as the suspect in the Brown University mass shooting and the subsequent killing of an MIT professor.

The examination confirmed Neves Valente died from a gunshot wound to the head, and the manner of death was ruled a suicide. 

Based on forensic findings and investigative information available to date, authorities estimate he died Tuesday, Dec. 16. Neves Valente was found dead in a storage facility in New Hampshire two days later on Thursday evening.

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Neves Valente was publicly identified by Providence police as the suspect in the Dec. 13 shooting at Brown University, which occurred during a finals week study session and left two students dead. Nine others were wounded at the Barus & Holley Engineering Building.

Authorities later confirmed he was also the suspect in the Dec. 15 fatal shooting of MIT nuclear science professor Nuno F.G. Loureiro, who was found shot at his home in Brookline, Massachusetts.

Federal investigators also recovered two 9 mm pistols in New Hampshire near Neves Valente’s body, according to the Bureau of Alcohol, Tobacco, Firearms and Explosives’s Boston office.

The ATF and FBI, working through the Connecticut State Police forensic laboratory, positively matched one of the guns to the weapon used in the Brown shooting. The second gun was matched to Loureiro’s killing, authorities said.

According to Brown University President Christina Paxson, Neves Valente was a Portuguese national and former Brown student who studied physics from the fall of 2000 through the spring of 2001 before withdrawing from the program in 2003. He had no recent affiliation with the university at the time of the shooting on campus.

“I think it’s safe to assume that this man, when he was a student, spent a great deal of time in that building for classes and other activities as a Ph.D. student in physics,” Paxson said. “He has no current active affiliation with the university or campus presence.”

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Neves Valente was found dead Thursday evening after law enforcement officers breached a storage unit in Salem, New Hampshire, where he was believed to be hiding. Authorities said he acted alone in both attacks.

During the investigation, law enforcement canvassed neighborhood surveillance video, released images of a person of interest and initially questioned, but later ruled out, another individual before identifying Neves Valente as the suspect.

The two Brown students killed were Ella Cook of Alabama and Mukhammad Aziz Umurzokov of Virginia. Several surviving victims remained hospitalized in stable condition.

Sources tell Fox News that investigators are continuing to examine Neves Valente’s recent movements, including tracing credit card transactions in the days leading up to the attacks. FBI agents are also in Florida, where he reportedly last lived, according to sources.

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Authorities have not found any writings or documents indicating a clear motive for the shootings.

Fox News Digital’s Andrea Margolis and Michael Ruiz contributed to this report.

Stepheny Price covers crime, including missing persons, homicides and migrant crime. Send story tips to stepheny.price@fox.com.