Riyadh   -  The former Saudi official’s tweet expressing condolences over an activist’s death seemed benign, but his mysterious disappearance soon afterwards highlighted what observers call the state’s “digital authoritarianism”.

Abdulaziz al-Dukhail, who had served as deputy finance minister, went missing in April along with at least two other public intellectuals also believed to be in detention for their implied criticism of the state.

In the following months, separate claims surfaced that a Twitter data breach by Saudi infiltrators in 2015 resulted in a wave of “enforced disappearances” of regime critics, many with anonymous accounts on the social media platform.

The cases illustrate how Saudi Arabia, which accounts for the most Twitter users in the Arab world, has sought to harness the power of the platform to promote its ambitious reforms while also aggressively seeking to tame free expression.

The three public figures dropped from view after expressing sympathy over the death of jailed activist Abdullah al-Hamid, according to family members and two campaign groups including the London-based ALQST.

Hamid, a veteran activist, died after suffering a stroke in detention while serving an 11-year sentence, sparking a torrent of criticism from international campaigners.

Dukhail’s exact whereabouts are not known and authorities have not revealed any formal charges, his son Abdulhakim al-Dukhail told AFP.

“Why was he taken? What was his crime?” said Abdulhakim, currently based in Paris.

“Is he in jail just for a tweet?”.

Saudi authorities did not respond to AFP’s request for comment.