Early on the morning of Sept. 25, three men walked out of a two-story building in Plaka, the old neighborhood at the foot of the Acropolis, carrying a length of copper pipe.
Security footage released by the police shows them strolling away, unhurried.
Hours later, the building exploded.
The blast on Lysikratous Street killed six people. Four were American tourists, two couples who had been due to fly home that afternoon.
The other two were an elderly British couple who lived upstairs. Investigators now say the pipe the men took, worth roughly 20 euros, or about $23, set the disaster in motion.
"We cannot believe our people were lost for 20 euros," relatives of the Americans said, according to the Greek state broadcaster ERT.
Prosecutors have charged the three men with homicide with possible intent, along with causing a deadly explosion, arson endangering human life and causing serious bodily harm. Under Greek law, the homicide charge applies when suspects foresee that their actions could kill and proceed anyway.
The case has struck a nerve in Greece, not only because of the trivial sum at its heart, but because of who the suspects are.
All three have long criminal records, mostly for theft, robbery and drugs, and all three had recently walked out of prison. One, with more than 20 prior cases since 2019, was released in March after serving part of his sentence.
Another, with 13 earlier cases, was freed in November 2025. The third, whose run-ins with the law date to 1985 and number around 45, was released on parole in June.
Fire service investigators said they had worked in strict secrecy before making the arrests.
On Friday, Giorgos Karapanos, a lawyer for the American families, joined the case as a civil party supporting the prosecution, giving the relatives a formal voice in the proceedings.
The three suspects are scheduled to testify before an investigating magistrate on Monday.
The explosion tore through one of the busiest tourist districts in Europe, shattering windows blocks away and damaging homes, shops and a nearby church.
The building where the victims died has since been demolished.
All three suspects are presumed innocent.