The man who 'disappeared' in Nigeria
A man who live-tweeted from the scene of an attempted jailbreak in the Nigerian capital Abuja 12 days ago, has disappeared.
Activists believe he may have been arrested, and have launched a Twitter campaign for his release.
The hashtag #FreeCiaxon and the Twitter handle @ciaxon have been trending in Nigeria since late on Wednesday.
There's also a lot of discussion about it on Facebook.
On 30 March, the man who runs the @ciaxon account found himself at the scene of a dramatic fight between Nigerian security forces and detainees trying to escape from the State Security Service (SSS) headquarters.
It was big news in Nigeria.
The SSS HQ is a stone's throw from the presidential palace, and the detainees were - according to officials - suspected militants from the notorious group, Boko Haram.
Official sources say more than 20 people were killed.
Much of the news came from social media sources at the scene - like @ciaxon.
It's believed Yusuf Siyaka Onimisi - also referred to as Isiaka Yusuf - runs @ciaxon.
He tweeted developments, including a series of images showing both the attackers and Nigerian soldiers.
The pictures were picked up by news outlets in the country.
But since then, there has been complete silence on Twitter from @ciaxon.
And the silence has not been just virtual.
Yusuf Siyaka Onimisi's brother Sanusi told BBC Trending that he has not been able to reach him since that day.
His car has been left abandoned.
"Nobody has given us any information.
We are in the darkness.
It's inhuman, it's very, very unfair," he says.
When a friend contacted Yusuf Siyaka Onimisi's workplace to ask where he was, he was told he had been arrested.
The SSS has not responded to confirm or deny Yusuf Siyaka Onimisi's detention.
But Nigerians have taken to social media to demand answers.
"How can you arrest people for taking pictures - this is the 21st Century," says Fola Lawal, a Nigerian now based in Qatar, who started the Twitter hashtag #FreeCiaxon.
"I would have done the same in his shoes.
It's called citizen reporting.
" Nigeria's National Human Rights Commission has started an investigation into his whereabouts.
High-profile figures, including the World Bank's former Africa vice-president Obiageli Ezekwesili, have tweeted calling for his release.
"It's very, very important this gets attention," says lawyer and writer Ayo Sogunro, who's been researching and tweeting actively about the case.
Critics say the government is trying to regulate social media.
The irony in this case, says Sogunro, is the tweets from the @ciaxon account were broadly supportive of the security forces.