On 5 August 2021, the lifeless body of Marco Alves Santo was discovered in the Rio Mondego River near the town of Figueira da Foz. It soon became apparent that the case was a homicide.

As the victim was a resident of Luxembourg and it could not be excluded that the perpetrator(s) also resided in the Grand Duchy, the public prosecutor's office of Luxembourg City opened a judicial investigation.
 
The investigation, conducted by the judicial police in close cooperation with the Portuguese authorities, led to the arrest of four people in the Grand Duchy on 9 March, the Luxembourg City public prosecutor's office announced in a statement on Tuesday.
 
They are the victim's life partner, her mother, the mother's boyfriend and the partner's son from a previous marriage. The four suspects were heard by an examining magistrate, who decided to remand the first three.
 
"The investigation is ongoing and numerous enquiries are still underway," the public prosecutor's statement said, reminding the public of the principle of presumption of innocence.