A 27-year-old man has been cautioned by police for sending "extremely offensive" Twitter messages to a Premier League referee.
Mark Halsey received the abusive tweets, which referred to his recent battle with throat cancer, after taking charge of Liverpool's 2-1 defeat against Manchester United on Sunday.
The 51-year-old - who sent off Liverpool midfielder Jonjo Shelvey before awarding United a penalty - made a complaint to Greater Manchester Police two hours after the game.
Police said a man from the Newcastle area admitted being responsible for some of the messages. He was cautioned for an offence committed under the Malicious Communication Act.
Officers say they are trying to trace anyone else responsible for posting the abusive messages. Both tweets, thought to have been sent by disgruntled Liverpool supporters, were met with outrage.
One, from an account named @johnwareing1, read: "I hope Mark Halsey gets cancer again and dies." The other, from @lfcjohn259, read: "Mark Halsey should've died of cancer."
Detective Sergeant Tony Lunt said: "Clearly the victim and his family were very distressed by the extremely offensive comments posted on Twitter. We take all reports of abuse on social networking sites very seriously as these remarks can and do have a devastating impact on people's lives."
The tweets came just days after the Director of Public Prosecutions said new guidelines for prosecutors on social media cases will be issued after a growing number of complaints.
Last week, a Welsh Premier League footballer who posted an abusive message about Olympic diver Tom Daley was not charged because the message was "not so grossly offensive that criminal charges need to be brought", Keir Starmer said.
But Mr Starmer, the most senior prosecutor in England and Wales, added: "The time has come for an informed debate about the boundaries of free speech in an age of social media."
Mr Halsey returned to refereeing in March 2010 after winning his battle against cancer.