President Donald Trump had blamed "sick" vandals, and a former Olympian had been charged, but prosecutors now say contractors caused the damage.
The US president's comments come after cyber attacks on Minnesota's water systems earlier this week, with US media indicating Iran could be behind it.
The economy grew at an annual rate of 1.5% in the three months to June, down from 2.1% seen in the previous quarter.
Investigators hope the notes' "distinct linguistic characteristics" may be recognised by a member of the public.
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Trump administration drops Reflecting Pool vandalism charge and admits 'botched' repairs
President Donald Trump had blamed "sick" vandals, and a former Olympian had been charged, but prosecutors now say contractors caused the damage.
Minnesota not Iran to blame for state's water issues, says Trump
The US president's comments come after cyber attacks on Minnesota's water systems earlier this week, with US media indicating Iran could be behind it.
US economic growth sees surprise slowdown in second quarter
The economy grew at an annual rate of 1.5% in the three months to June, down from 2.1% seen in the previous quarter.
'Our hearts are in ruins,' Savannah Guthrie says after kidnapped mother's ransom notes released
Investigators hope the notes' "distinct linguistic characteristics" may be recognised by a member of the public.