They also appear to violate the terms of use published by Twitter. It warns users: “You may not promote violence against, threaten, or harass other people on the basis of race, ethnicity, national origin, sexual orientation, gender, gender identity, religious affiliation, age, disability, or serious disease.”

Asked why the original tweets have not been deleted, a Twitter (TWTR, Tech30) spokesperson said:

“To help ensure people have an opportunity to see every side of an issue, there may be the rare occasion when we allow controversial content or behavior which may otherwise violate our rules to remain on our service because we believe there is a legitimate public interest in its availability.”