Elderly homeowner decided to break down the bricked up archway in his cellar after 60 years.

What was inside made him call the FBI with trembling hands.

80-year-old Arthur Wallace had lived in his Boston home for six decades.

Always wondering about the strange bricked up archway in his cellar.

Deciding to finally renovate, he grabbed a sledgehammer and started chipping at the mortar.

The wall was unusually reinforced, and after hours of work, he barely made a dent.

Arthur called his son David, who arrived with heavyduty demolition tools.

They worked relentlessly until an opening appeared, revealing a hidden chamber behind the bricks.

Pulling away the debris, they uncovered a room frozen in time.

Arthur aimed his flashlight into the darkness, illuminating wooden crates and strange diagrams pinned to the walls.

But the moment he saw what was stacked in the far corner, he immediately called the FBI with trembling hands.

The hidden room was a planning center for a domestic terrorist group from the 1960s.

FBI agents discovered stacks of bomb-making materials, still dangerously unstable after decades.

Pinned to the walls were detailed maps of Boston and a manifesto outlining a plot to attack a federal building that never came to fruition.

Authorities evacuated the neighborhood while specialized teams carefully neutralized and removed the explosives.

Investigators concluded the group disbanded abruptly, sealing their headquarters before disappearing completely.