The mayor of Naples has joined human rights groups in calling for “truth and justice” following the death of an Italian United Nations volunteer who had been on a peace mission in Colombia. Mario Paciolla, 33, from Naples, was found dead on 15 July at his home in San Vicente de Caguán, a town in Colombia’s southern jungle long used as a strategic rearguard for rebel groups and drug traffickers. “We embrace his family and assure them of our support for truth and justice,” Luigi de Magistris, the mayor of Naples, told AFP on Thursday. Colombian authorities said Paciolla, who also worked as an investigative journalist, had killed himself but family and friends are skeptical. “We want the truth. Our son was very afraid,” Anna Motta, Paciolla’s mother, told La Repubblica. “It is not possible that our Mario, a brilliant traveler of the world and UN observer took his own life.” Motta said that during his last days, Paciolla had been worried about “something he had seen”. Luigi Corvino, a lifelong friend of Paciolla, told the Guardian: “He was the kind of person that really wanted to make the world a better place and had the skills, experience and the attitude to do it. Someone took it away from him, and I think the world owes him at least the truth.” In a letter to Paciolla published in El Espectador on Wednesday, the investigative reporter Claudia Julieta Duque described her deceased friend as “always laughing in the face of the absurd”. Duque also expressed doubt that Paciolla had killed himself, writing that “your love for yourself contradicts the idea that you were capable of ending your life in a place so far from your friends, family and loves, and from Naples”. De Magistris and rights groups have joined calls for an investigation into Paciolla’s death, which they compared to the unsolved murder of the Italian doctoral researcher Giulio Regeni, who was tortured and killed in Egypt in 2016. The Italian foreign minister, Luigi Di Maio, told parliament on Wednesday that the details of the case are “unclear”, adding that an autopsy, jointly arranged by Italian authorities, should shed light on what happened. “I assure maximum commitment from the foreign ministry and my staff for a case involving a brilliant young man engaged in a delicate mission,” he said. A group of Paciolla’s friends have launched a petition, calling on the foreign minister to see that justice is served. Paciolla was a member of a UN mission overseeing the implementation of a 2016 peace deal signed between the Colombian government and the Revolutionary Armed Forces of Colombia (Farc), a Marxist rebel group. That deal formally ended 52 years of civil war that left 260,000 dead and forced 7 million to flee their homes. But implementation of the accord has been checkered with violence as Farc dissidents, rightwing paramilitaries and organized crime groups still fight for territory. On the same day that Paciolla was found dead, an entire village of demobilized Farc fighters was relocated by the government following the murder of 11 of its residents since the deal began to be implemented. The European commission spokeswoman, Nabila Massrali, said on Thursday that the EU was closely following the situation. “It is obviously important that the facts are established and that the necessary investigations are carried out by the Colombian authorities,” she said.