An MP has asked Twitter's CEO Jack Dorsey to "explain himself" after a police inquiry into a "racist death threat" was halted when the social media giant did not co-operate.
The Metropolitan Police said they had been unable to get details from Twitter of the account which sent the tweet to Tottenham MP David Lammy.
Mr Lammy tweeted Mr Dorsey asking why Twitter was "shielding vile racists".
Twitter said it was now co-operating with the police inquiry.
Earlier on Wednesday the Met said a "thorough investigation" had been carried out into the tweet.
'Push race hate'
A spokesman said: "All lines of inquiry were explored as far as possible, however, due to the owner of the suspected social media account living outside the UK and the fact we were unable to obtain the subscription details of the individual from Twitter, we were unable to continue the investigation."
Mr Lammy reacted to the Met's announcement by tweeting direct to Mr Dorsey.
He tweeted: "Please explain why you are shielding vile racists who make death threats on your platform? #BlackLivesMatter.
"You should not be able to push race hate and send death threats with impunity online.
"Shame on Twitter for failing to act with Met Police to identify who sent this threat.
"#BlackLivesMatter has to be more than a slogan to drive traffic and ad revenue on your website."
A Twitter spokesperson later said it was co-operating with police "having now received and processed the correct information".