A police force has spoken to four teenagers who sent racist and threatening tweets to ex-footballer Stan Collymore but said it had been unable to track down other abusive users after Twitter failed to supply their details.
Staffordshire Police said it had been unable to trace others who had sent abusive messages because the social networking site had been unable to pass on their details.
It comes after Mr Collymore reported receiving racially abusive and threatening tweets between January and May.
Mr Collymore tweeted on Monday: "Cannock and Staffordshire Police have been exceptional.
"It's Twitter refusing to give info. Twitter, beyond UK law. For now."
Chief Inspector Steve Morrey, commander of Cannock Chase Local Policing Team (LPT), said: "A thorough and detailed investigation was launched by Staffordshire Police following the abuse directed at Mr Collymore on Twitter earlier this year.
"After inquiries were carried out four juveniles were located and dealt with through restorative justice. Mr Collymore was aware of this and happy with the process.
"Despite repeated requests for information made to Twitter regarding a number of other users we wanted to speak to in connection with this matter Twitter have not supplied it.
"We have also tried to obtain this information via other social media networks but to no avail. Therefore all lines of inquiry have been exhausted. The matter will be reviewed should any new information come to light.
"Mr Collymore has been regularly updated on our progress throughout this investigation and is aware of the outcome.
"We would like to reiterate the abuse directed at Mr Collymore was completely unacceptable and we all have a shared responsibility to treat each other with dignity and respect.
"It's our role to investigate complaints of criminal behaviour and where appropriate take action."
On their website Twitter says : "(We) have a clear process for working with the police and are in ongoing communication with relevant UK police forces to make sure they are aware of our policies
"Twitter is an open communications platform. Our priority is that users are able to express themselves, within acceptable limits and, of course, within the law. We cannot stop people from saying offensive, hurtful things on the Internet or on Twitter. But we take action when content is reported to us that breaks our rules or is illegal."
A spokesperson for Twitter said they were working to eliminate abuse but said : "We do not comment on individual accounts, for privacy and security reasons."