German police are investigating an overnight fire that spread into a substation in central Berlin. Hours later, officers in western Germany found a cut fence at another substation, according to the tabloid Bild, as reported by iROZHLAS and iDNES.

The incidents follow several attacks on German substations last week that police are investigating as sabotage, per iROZHLAS. Investigators are hunting a 48-year-old man who claimed responsibility in letters but have not found him.

The Berlin fire did not disrupt power supply, and its cause remains unknown. Media have linked it to last week's sabotage wave, but that connection is unconfirmed, according to Seznam Zprávy.

HYPOTHESIS: A cluster of substation fires, cut fences and anonymous claims of responsibility fits the profile European security officials have flagged as hybrid-war sabotage against energy infrastructure. Supporting this: the incidents are clustered in time, target the same type of site, and include a claimant communicating with authorities. Against it: none of the source reporting names a state actor, the Berlin fire's cause is still unconfirmed, and the letter-writer's motive and identity remain unknown — this could just as easily be a single actor unconnected to any foreign campaign.

What to watch: whether investigators find a cause for the Berlin fire and catch the 48-year-old suspect — either would show whether Germany faces one actor or a coordinated campaign.