Saudis near a portrait of Saudi Crown Prince Mohammed bin Salman at the Dubai World Trade Center in Dubai on Tuesday. (Karim Sahib/AFP/Getty Images)

TO UNDERSTAND the police state in Saudi Arabia, consider the case of Essem Al-Zamel.

An economist and entrepreneur, as well as a social media star, Mr. Zamel last year criticized a plan by Crown Prince Mohammed bin Salman to offer shares to investors in the national oil giant, Saudi Aramco. That was meant to be a dazzling event, another audacious idea in the crown prince’s blueprint to modernize and diversify the kingdom. But Mr. Zamel said the valuation was so high as to imply selling all the country’s oil reserves for the next two decades, or more, and he declared on Twitter, “It is neither fair nor logical to sell the oil from under our feet in a commercial transaction at this juncture.” At least, he wanted a public debate.

But there is no such public debate in Saudi Arabia, and Mr. Zamel was soon swept up in a dragnet of Saudi journalists, clerics, academics and others. Though the crown prince eventually abandoned the Aramco deal, Mr. Zamel was severely punished, accused of belonging to a terrorist organization, meeting with foreigners and posting tweets “prejudicial to public order,” among other things. He remains in prison.

The kingdom has long been an absolute monarchy that does not tolerate open dissent, but this kind of repression is new. In earlier times, Saudi rulers restricted behavior, often under severe interpretations of Islamic law, and carried out barbaric punishments. We have often called attention to the unjust treatment of blogger Raif Badawi, who was arrested in 2012 and sentenced to 1,000 lashes — 50 were delivered in a public square in Jeddah before it was stopped — and 10 years in prison for online posts that challenged the religious authorities to allow a more pluralistic and moderate practice of Islam. The system was intolerant and harsh.

But the old system allowed limited channels to express opinions. Those channels have been choked off under the reign of King Salman, who took over in 2015, and his son, Mohammed, who became crown prince in June 2017.

The new rulers reorganized agencies and rewrote the laws on counterterrorism — a legitimate security concern — to gain more power to quash dissent and imprison people for long periods on the slightest pretext. The crown prince purged his cousin, Mohammed bin Nayef, who controlled the interior ministry, and the ministry was stripped of its powers in intelligence and counterterrorism. In its place was created a powerful new agency, the Presidency of State Security, which reports directly to the king and can conduct “search, investigation, seizure, criminal and administrative prosecution” without judicial oversight, according to a U.N. Human Rights Council report.

Almost all prosecutions of political and human rights activists have been channeled through the Specialized Criminal Court, originally established in 2008 to handle terrorism cases, where defendants often do not have lawyers during the investigative phase, and pretrial detentions can be arbitrary and lengthy. In October 2017, the kingdom updated its counterterrorism law, which was already overly broad, to add a host of tripwires to criminalize free expression. For example, the definition of terrorism was extended to those who “describe” the king or crown prince “in any way offensive to religion or justice.”

A good example of how the environment has changed is the case of female activists who had long sought the right to drive, and to change the guardianship system, which gives men the authority to make critical decisions on behalf of their female relatives. For years, the women had carefully pushed for change while staying largely within bounds the government could accept. But the new crown prince could not tolerate their voices. He granted women the right to drive — and then punished those who had worked for that reform. In May, 11 of them were arrested. Several remain in jail, accused of serious crimes that could bring long prison sentences, including “suspicious contact with foreign parties” and undermining the “security and stability” of the state. They have been vilified in the media; a pro-government Twitter account posted images of those arrested with the word “traitor” splattered in red across their faces, Human Rights Watch reported.

In March, one of the women, Loujain al-Hathloul, was forcibly wrested from her car in the nearby United Arab Emirates, where she was studying, and brought back to Saudi Arabia. Her husband, Fahad al-Butairi, a well-known Saudi actor and comedian, was working in Jordan when security officers arrested him there; he was handcuffed, blindfolded and put on a plane to Saudi Arabia. She was freed, but then arrested again, and remains in prison.

The jails of Saudi Arabia in fact are now brimming with people ensnared in the crackdown launched by the crown prince. Among them are 11 founders of the Saudi Civil and Political Rights Association, sentenced to a total of nearly 200 years in prison and travel bans, according to the London-based human rights group ALQST. Altogether, that group estimates, more than 400 people were detained in 2017, the first year the crown prince was in office. They include journalists, activists, clerics and businessmen.

This is the backdrop to the Oct. 2 disappearance of Jamal Khashoggi, a contributor to The Post’s Global Opinions section, who entered the Saudi Consulate in Istanbul and has not been seen since.

Mr. Khashoggi was a keen observer and critic of this tightening. He described in his Post columns how the crown prince retained an information blacklist intended to chastise and intimidate writers who offered any criticism of the regime. And he understood that setting people free to think and to express themselves would be a far greater source of strength for Saudi Arabia than gagging, imprisoning, kidnapping and killing them.