As investigators in Massachusetts work to piece together a motive for the murders of two Brown University students and an MIT physics professor, former classmates of the suspected gunman and one of the victims have been asking if the roots of the tragedy lie in their shared experience at a top university in Portugal.

The suspected gunman, Cláudio Valente, and one of those killed, Nuno FG Loureiro, studied at the prestigious and notoriously challenging University of Lisbon engineering and technology school, known locally as Técnico, both graduating in 2000.

Contemporaries of the two men describe the academic environment as emotionally gruelling. Only one was willing to go on the record, but several others expressed similar opinions.

Valente was described as brilliant and competitive, but willing to help his colleagues out. He finished top of his class, with an average grade of 19 out of 20, an unusually high score for Técnico. Loureiro, who was said to be an excellent student but more easygoing than Valente, finished with an average grade of 16 out of 20.

Classmates say that, at the time, the two men appeared socially well adjusted.

Nuno Morais, 48, now a researcher at the Gulbenkian Institute for Molecular Medicine in Lisbon, said he and his fellow classmates, shaken by the news of Loureiro’s killing, had been “racking their brains” for any signs that something was wrong.

“Having known Cláudio and having had a good relationship with him, we can’t find any other explanation than a serious mental health problem – exacerbated by resentment for not having achieved the academic career he dreamed of,” he said.

Soon after his graduation in Lisbon, Valente enrolled at Brown University as a promising young doctoral student of physics, but dropped out after a few months in early 2001 and returned to Portugal to work as a programmer for an internet provider.

Loureiro studied at Imperial College London and then Princeton University, later working at the UK’s Culham Centre for Fusion Energy. He joined MIT in 2016 as a professor of nuclear science and engineering, eventually becoming the director of the Plasma Science and Fusion Center at the institute.

Valente and Loureiro’s classmates said they suspected that the highly competitive atmosphere of academia may have taken a mental toll.

“I don’t remember any specific situations directly involving Nuno and Cláudio during our graduate degree, but the culture in these schools remains the same – a hyper-competitive environment where students who struggle are humiliated and made to feel they can only succeed if they are the best of the best,” said Morais.

According to his peers, Valente was crushed by his failure to complete his PhD.

Morais said: “The only connection I can make with Cláudio’s trajectory and what happened was his disappointment with the experience at Brown. Those of us who work in academia dream of pursuing a PhD at a major American university. Cláudio aspired to have a brilliant academic career, comparable to Nuno’s, and this dream was prematurely destroyed, generating frustration.” .

He said his current work included mentoring and supporting students, which had made him aware of how normalised emotional distress and high pressure are in academia. He said that over the years higher-education institutions such as MIT and Caltech had taken steps to relieve student pressure because of high suicide rates. Portugal lags on this matter, he said.

“Portuguese schools now have therapist offices to assist students, but there’s a great delay in fighting bullying and harassment inside the institutions. The prevailing culture is still one in which senior figures behave in ways that are prejudicial to mental health and that continues to be tolerated. Tragedies like this should prompt us to think very carefully,” Morais said.

A spokesperson for Técnico said the school was not aware of any connection between the shootings and Valente and Loureiro’s time at the university.

“From what we have been reading in the media, they seemed to have a normal, collegial relationship. We are unable to see how something that happened 30 years ago can be connected to what happened now, but the school is going to come together to reflect and discuss,” they said.

Valente returned to the US in 2017 through the diversity lottery immigrant visa programme and was granted a green card. He was living in Miami.

On Friday morning, after Valente was found dead in a storage facility in Salem, New Hampshire, the homeland security secretary, Kristi Noem, announced she had paused the visa scheme under Trump’s direction to “ensure no more Americans are harmed by this disastrous programme”.

“This heinous individual should never have been allowed in our country,” she wrote in her social media statement.

Such comments, and the Trump administration’s subsequent move to further narrow the pathways to legal immigration using the crime as a pretext, caused outrage among Valente and Loureiro’s peers.

Morais said: “[This puts] the focus of the problem in the wrong place. Access to weapons and the hyper-competitive culture of some universities are closer to the root causes of these shootings than migration.”