In the wake of the killings in Isla Vista, it emerged that Elliot Rodger, the perpetrator, frequented "men's rights" forums.
Some people on social media appeared to express sympathy for Rodger.
In response, #YesAllWomen began to trend on Twitter last night. The hashtag began as a response to traditional male rights' activists complaints such as "friend-zoning".
But now wider concerns are being aired. They include harassment — physical or otherwise...
...and gender relations, among others.
At the time of writing, the hashtag was the top trend on Twitter with nearly 150,000 people using it.
Not all of the tweets were written by women.
It forms a counterpoint to the "Not All Men" meme that grew in popularity earlier this year.
Note: BuzzFeed has received permission from all those featured in this post to use their tweets.
An earlier version of this post said Roger shot dead three women after stabbing three men to death. In fact two women and one man were shot dead. Thirteen other people were injured, eight of them from gunshot wounds and four others by blunt trauma sustained after being struck by the attacker's vehicle.