Police cybersecurity chief Yavor Kolev said Wednesday a 20-year-old Bulgarian employee of a cybersecurity company is suspected in the hacking.
The leak is the biggest in the Balkan nation so far. Local media say the details of some 5 million of the country's 7 million people were stolen.
Kolev said the investigation is still ongoing and other people could have been involved.
Prime Minister Boyko Borissov said the well-educated suspect was trying to prove his computer skills. Borissov added the suspect was a credit to Bulgaria's education system but he should have been working for the state instead of causing harm.
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