Diogo Alves, the Aqueduct Killer

A Galician migrant in Lisbon

Diogo Alves was born in 1810 in Galicia, in the north-west of Spain, in the province of Lugo. Like many Galicians of his time he moved to Lisbon while still very young, looking for work. He found employment in well-off households and worked as a coachman. His name has since become attached to one of the most enduring crime stories in Portugal, but historians and journalists who have looked closely at the case stress that the story has two layers: a documented criminal trial that ended in his execution, and a much larger body of legend that grew up around it.

The aqueduct stories

Alves is remembered above all as the "Aqueduct Killer", after the Águas Livres Aqueduct, the great eighteenth-century structure that carries water into Lisbon across the Alcântara valley. Popular accounts say that between about 1836 and 1839 he lay in wait on the public walkway along the top of the aqueduct, robbed people crossing it, many of them poor traders and farmers taking goods into the city, and threw them to their deaths. At first the authorities took the deaths for a wave of suicides. Rising numbers of deaths in the valley caused alarm, and the walkway was closed to the public in 1837. Figures of more than 70, or even more than 100, victims are often repeated. These numbers come from later retellings, not from any court record, and a 2014 academic study of the case calls the figure of 70 very probably false. No investigation was ever opened against Alves for the aqueduct deaths, and he was never tried for them, so the true number of victims, if any can be linked to him, is unknown.

The crime he was tried for

What the courts did examine was a robbery at the home of a doctor named Andrade on Rua das Flores in Lisbon, which took place after the aqueduct route had been closed. By then Alves led a gang, most of whose members, like him, were Galician. The doctor was away that night. A servant in the house let the gang in, and the people inside were killed: a widow, whose exact relationship to the doctor is described differently in different accounts, her two daughters, and her son, a student from Coimbra who was visiting. The servant who had opened the door later regretted his role and was himself killed by the gang. Accounts of the arrest differ: one says a member of the group gave Alves up, while a 2014 study says police reached the gang by following a trail left by the murdered servant.

Trial and execution

The witnesses at the trial included a tobacconist whom the gang had also robbed and the eleven-year-old daughter of a woman linked to the gang. Alves was sentenced to death, as were several associates, including António Martins and men known by the nicknames Palhares and Beiço Rachado. A woman named Gertrudes Maria, called "a Parreirinha", a tavern keeper described in popular accounts as his lover, received a sentence of perpetual exile to Portugal's African colonies along with other members of the group. Alves was hanged in Lisbon in February 1841, on the same day as Martins. He is often called one of the last people put to death in Portugal, and other hangings followed in the 1840s.

The preserved head

After the execution, Alves's head was given to doctors at Lisbon's medical school, then the Escola Médico-Cirúrgica, so that it could be studied for signs of a supposed inclination to crime. It was preserved in a jar of formaldehyde and is still held by the Faculty of Medicine of the University of Lisbon. In 2017 it was lent to an exhibition in Coimbra marking the 150th anniversary of the abolition of the death penalty. Later analyses of the skull relied on craniometry and the racial theories of their time, which claimed to find anomalies in it.

Legend, literature and film

Alves's story spread through cheap popular pamphlets in the nineteenth century, which often blamed his companion Parreirinha for leading him astray and used the case as a moral warning; a 2014 study also notes the prejudice against Galician migrants in these texts. Some well-known episodes, such as the tale of a child who smiled at him before being thrown from the aqueduct, appear only in fiction and cannot be verified. In 1911 the story became the film Os Crimes de Diogo Alves, directed by João Tavares, which premiered in Lisbon on 26 April 1911 and has been called the first great Portuguese fiction film; police suspended screenings over fears it could encourage crime.

Why the case matters today

The case shows how a real conviction for a household robbery and murders can become a much larger myth. It also belongs to the history of capital punishment in Portugal, which abolished the death penalty for civil crimes in 1867, partly after public unease over botched executions such as one in Tavira in 1845. Interest continues: in September 2025 Prime Video and the broadcaster TVI announced Lisbon Noir, a fictional police thriller about a modern killer who imitates the methods attributed to Alves.