JEDDAH, Saudi Arabia (Reuters) - Outside a villa surrounded by palm trees on the outskirts of Saudi Arabia's second largest city Jeddah, police cars guard an exceptional criminal court where 16 men were put on trial this year after more than four years detention.
The men face charges of "funding terrorism" and coordinating with al Qaeda to take power along with a host of other charges finally pressed last year.
Rights activists say the prisoners -- from well-known Saudi families, including professors and a former judge -- were really seized for refusing to heed Interior Ministry warnings to give up political activism and were planning to set up a political party.
"My father is a person who cannot be silent about what is wrong, whether it is in the street, in our house or in society," Eman al-Shemairi, the daughter of one of the men, said in a video put up on YouTube in March.
But the Jeddah detainees are more fortunate than many.
Thousands of people have disappeared into the black hole of Saudi prisons without charge or any indication of when they could be released, Saudi and international rights groups say.
The government says it is an Islamic state ruling via Islamic Sharia law, according religious scholars wide powers in society and an advisory role to the Saudi royal family, which accords itself a benevolent paternal role.
Activists say the result is that security forces can act with impunity, and defendants are subject to an individual judge's interpretation of Sharia law and in many cases are not allowed access to their lawyers.
Without a penal code, there is even confusion over definitions, including what "detentions" and "political prisoners" are.
Saudis can find themselves in a revolving door of detention, release and detention, making it hard to clearly call someone a detainee or to track numbers.
And in a system where there is no room for political parties or democratic political processes, there is no concept of a political crime, and therefore no political prisoners.
The long reach of security forces, with a free hand to detain at will, was a major complaint of protesters who took to the streets in Tunisia and Egypt earlier this year, toppling veteran rulers and sending shockwaves throughout the region.
The government says that would not happen in Saudi Arabia because of its Islamic system and the popularity of King Abdullah, in his mid-80s, though it is unclear how much of that popularity has filtered down to the rest of his family.
"We reiterate that there are no political prisoners in the kingdom," Interior Ministry spokesman Mansour al-Turki said.
The ministry said 5,696 people had been detained by the authorities in "militant" cases, adding that 5,080 of them had now appeared before courts as the authorities try to get through a backlog of people detained since at least 2003.
Saudi Arabia began battling al Qaeda militancy in 2003, detaining thousands on suspicion of links to militant groups, but dozens were also detained earlier this year following small pro-democracy protests and gatherings in the Eastern Province.
Protesters gathered outside the Interior Ministry in Riyadh to demand the release of relatives in March.
Saudi Arabia also has a "morality police" apparatus run by the powerful clerical establishment in coordination with the Interior Ministry, meaning it is possible that some state security detainees are being held for suspected crimes against Islam such as insulting the Prophet Mohammad, denigrating the Quran or "sorcery."
The independent rights groups say there could be anything from 12,000 to 30,000 people in those Saudi prisons which are used specifically for cases involving national security issues.
The independent Saudi rights body Human Rights First puts the number of security apparatus detentions at between 12,000 and 15,000, its head Ibrahim al-Mugaiteeb said.
"We monitor statements from the Ministry of Interior ... but for thousands of the people arrested we find out about them from their families," Mugaiteeb said.
The Saudi Civil and Political Rights Association (ACPRA) says it believes that all prisons connected to the Directorate of General Investigations (DGI), the state security apparatus, are full, which would put the total held at around 30,000.
Last week it sent a public letter to the Interior Minister Prince Nayef detailing cases where it said security offences had been fabricated to justify arrests of political activists but many had simply fallen foul to the whims of security officers.
UK-based Amnesty International says it estimates the number of people who have been detained in the thousands, some for criticizing government bodies and others for security reasons.
"There is a high level of secrecy maintained by the security in Saudi Arabia which makes it difficult for human rights organizations to have a precise number and details of people detained," said Dina El-Mamoud, an Amnesty researcher.
"We know that thousands have been arbitrarily detained in Saudi Arabia since 2001," she added.
Saudi Arabia is in the process of studying new terror legislation that was criticized by Amnesty in July after it obtained a copy of the draft Penal Law for Terrorism Crimes and Financing Terrorism and published it on its website.
If passed, the new law would allow suspects accused of "endangering ... national unity" and "harming the reputation of the state" to be held incommunicado indefinitely as terrorism suspects, if approved by a special court, the draft said.
The law would also stipulate a minimum 10-year jail sentence for questioning the integrity of the king or crown prince.
The ACPRA says the special courts are an infringement of rights in themselves.
"These courts violate the rights of defenders and prisoners, document forced confessions extracted under torture and coercion," it said this month.
Editing by Andrew Hammond and Sonya Hepinstall