A Sudanese church leader has been released but three others – a fellow pastor, an aid worker and a graduate – continue to face the death penalty or life imprisonment for seven criminal charges relating to alleged "spying".

Of the four men detained since December 2015, Kuwa Shamal was released after a hearing in Khartoum yesterday, during which the judge concluded that there was insufficient evidence to charge him, according to World Watch Monitor (WWM).

However, the judge ruled there was sufficient evidence to proceed with the trials of fellow Sudan Church of Christ leader Hassan Taour, Darfuri graduate Abdulmonem Abdumawla and Czech aid worker Petr Jasek, WWM reported.

After months of what WWM called "stagnation", several hearings have taken place in recent weeks and the next hearing is scheduled for 9 January, when the defence lawyers will present their case.

Shamal and Taour were both unable to attend a hearing on 19 December due to ill health, WWM said. During that hearing, the judge dismissed one of the prosecution witnesses – a member of the National Intelligence and Security Service (NISS) – after complaints from the defence that the witness's testimony added nothing extra to that of a previous NISS official.

Further witnesses were heard on 26 December and 28 December and the defendants each gave statements and were questioned by the judge.

The accusations against the remaining three men include waging war against the state, inciting hatred between classes, propagating false news, espionage and complicity in criminal agreements.

The defendants are specifically accused in the court indictment of "fabricating videos or incidents of claimed genocide, killing of civilians and burnings of villages, besides claims of persecutions of Christians in Sudan".

After Taour and Shamal were arrested by the NISS on 18 December last year, they were held "incommunicado" for months, without charges or contact with their families, WWM reported.

Abdumawla, a single man employed in a mining exploration company in Khartoum, was reportedly arrested just a day earlier, after Jasek had been taken into custody on 10 December, when authorities confiscated his computer, mobile phone and flash drives as he sought to leave the country.

All four were transferred to the Omdurman prison in early August and then formally indicted before the Khartoum North Court on 21 August, according to reports.

Court proceedings have since been scheduled almost weekly, but repeatedly postponed without warning when a witness, translator or the judge failed to appear.

Western diplomatic observers have periodically sat in on the trial hearings, with local supporters gathering outside the court at times to sing hymns and shout encouragements to the defendants.

According to WWM, one observer at a hearing last month said: "The prosecutor has nothing new. It was just a repetition of what has already been said... They didn't have any evidence to support their accusations."

In December, questioning in court focused on allegations that a meeting Taour and Shamal had attended with other Sudanese church leaders in Ethiopia a month before their arrest was organised with political motives to "damage and tarnish" Sudan's international image.

Though the NISS officer serving as the plaintiff in the case to answer some questions posed by the defence lawyers, he also declared that "national security considerations" overrode several of Sudan's criminal procedure laws that had been violated throughout the past year.

The European Parliament in early October adopted an Urgency Resolution, calling for the "immediate and unconditional" release of the four men on trial "on charges of highlighting alleged Christian suffering in war-ravaged areas of Sudan".

Since 1999, the US State Department has designated Sudan as a "country of particular concern" for ongoing religious freedom violations, including the treatment of Christians. Sudan is ranked 8th in the Open Doors World Watch List of the 50 countries highlighted for persecution against Christians.