Samsung smartphones caught fire because of battery failures
Samsung has said failures in the design and manufacturing of the batteries in its Galaxy Note 7 caused them to overheat and catch fire.
The Korean electronics giant was forced to recall three million handsets after the dangerous defect appeared within weeks of its grand launch in August.
The manufacturer launched a vast inquiry into what was behind the problem that is expected to cost the company an estimate 5.3 billion dollars (£4.3 billion).
Around 700 Samsung engineers carried out tests on 200,000 handsets and 30,000 batteries that were charged and drained over several months.
Koh Dong-Jin, president of Samsung electronics mobile communications business told a press conference in Seoul: "We found that both fully assembled devices and batteries exhibited incidents at similar rates to those in the field.
"This indicated that the incidents were caused by the battery cell itself and we preceded to focus our investigation on the batteries."
Mr Koh said he "deeply apologised" to Samsung customers and the company's partners, adding that the public post-mortem was "a first step to regain your trust".
Soon after the Galaxy Note 7 launched, videos were posted on social media from owners around the world of handsets appearing to overheat and burst into flames .
Two weeks later Samsung announced a global product replacement scheme, but was forced to elevate it to a full recall when the replaced handsets exhibited the same fault.
Of the three million handsets sold between August and October, 96% had been returned, Mr Koh said.
The company carried out its own investigation on the Note 7's manufacturing and distribution logistics processes and drafted in specialist companies to carry out independent tests.
Experts analysed third party apps to see if they had an effect on how the device operated, tested the water resistance of components and even subjected the charging components to a 4,000 volt static shock.
"None of these tests demonstrated abnormality or correlation to the reported incidents," Mr Koh said.