Dutch police have questioned a security researcher who said he successfully logged into the US president's Twitter account by guessing his password, reports BBC.
Last month, well-known cyber investigator Victor Gevers said he had gained access to Donald Trump's Twitter account with the password 'MAGA2020!'.
The White House denied it had happened and Twitter said it had no evidence of a hack.
But Gevers has now revealed more information to back up his claims.
As part of the police interrogation, Gevers revealed for the first time that he had substantially more evidence of the "hack" than he had previously released.
He did not reveal exactly what information he had, but by logging in to somebody's Twitter account someone would in theory be able to:
see and send private messages
see tweets that the user had privately bookmarked
access information such as how many people the account holder had blocked
They would even be able to download an archive of all the user's data, including photos and messages.
A spokesman for the Dutch Public Prosecution Service confirmed to De Volkskrant newspaper: "We are currently investigating whether something criminal has happened."
The spokesman said their inquiry was an "independent Dutch investigation" and not based on a US request for legal assistance.
The police told the BBC that Gevers had been questioned as a witness by the High Tech Crime Team and was not a suspect yet.
Police must first prove that the hack happened. If prosecutors consider Mr Gevers' actions to be illegal and outside the realm of cyber-security research, he could face up to four years in prison.
Gevers told reporters of his hack on 22 October. Dutch news outlet Vrij Nederland first reported the story.
Donald Trump's Twitter account has about 89 million followers.