Counterterrorism police have arrested a fourth suspect in the investigation into the fatal firebomb attack on the Thessaloniki home of former New Democracy parliamentary candidate Afroditi Nestora, an assault that claimed the life of her mother, Vagia Nestora.

The 25-year-old suspect was arrested during a counterterrorism operation in the Ano Poli district of Thessaloniki as he was leaving his residence. Authorities believe he played a pivotal role in the case by obtaining the keys to an apartment allegedly used as a “safe house” by the suspected perpetrators before and after the July 1 attack.

Counterterrorism officers sealed off the street outside the apartment building before conducting an extensive search of the suspect’s second-floor apartment.

Investigators removed two sealed fuel containers from the residence, which are being examined to determine whether they contained flammable liquid that could be linked to the attack. Officers also seized mobile phones and other digital evidence for forensic analysis.

According to police, the suspect, an electrician, was already known to authorities following an earlier arrest with his brother in a vandalism incident involving damage to storefront windows.

Investigators describe the 25-year-old as a key intermediary in the case, while alleging that he was acquainted with the 24-year-old owner of the apartment.

The latter has reportedly told investigators he handed the keys to the 25-year-old without knowing they would ultimately be used by individuals allegedly involved in the firebombing.

The latest arrest expands an investigation that has already resulted in the detention of three other suspects, including a 29-year-old man and a 26-year-old woman accused of carrying out the attack, as well as the apartment owner accused of providing the property allegedly used as an operational base. According to reports over the past two weeks, counterterrorism investigators believe the apartment was used for surveillance of the target and as a hideout before and after the attack, with evidence including security camera footage, telecommunications data and forensic material forming the basis of the case against the suspects.

The July 1 coordinated attacks targeted the homes of three New Democracy officials in Thessaloniki.

The device placed outside the Nestora family residence ignited a fire that fatally injured 72-year-old Vagia Nestora and also injured her daughter, her father and two other residents of the apartment building.