Families of passengers who rebelled against hijackers aboard United Airlines Flight 93 said today the FBI theory that the terrorists deliberately crashed the plane into a Pennsylvania field was based on ”limited and questionable interpretations” of the cockpit recording.

Even as they scrambled to flee World Trade Centre offices, workers paused to count heads, making sure their deskmates were there.

The US plane hijackers murdered stewardesses with knives to draw pilots from their cockpits, it emerged today as investigators began to piece together the full horror of the worst terror attack in history.