Mr El-Zakzaky and his wife were arrested in December 2015, after the Nigerian Army extra-judicially killed over 300 followers of the Shiite cleric.
Last Wednesday, a Kaduna State High Court acquitted the leader of the Islamic Movement in Nigeria (IMN), Ibrahim El-Zakzaky, and his wife Zeenat.
The couple were charged to court by the Kaduna State Government for their alleged roles in the death of a soldier in December 2015.
The court upheld the no-case submission filed by the counsel to Mr El-Zakzaky and his wife; indicating the state could not prove that the couple had committed any offence.
For the most part of the detention period, Mr El-Zakzaky and his wife were held at an undisclosed location by the State Security Service (SSS).
The origin of the clampdown was a demonstration by members of the group, on a major road in Zaria, during which they blocked the convoy of the then chief of army staff, Tukur Buratai, and other road users.
The Nigerian Army accused Mr El-Zakzaky and his followers of attempting to assassinate Mr Buratai, but the Islamic movement said soldiers simply attacked "defenceless people."
Sani Usman, the then army spokesperson, called the incident unfortunate, few days after it happened, adding that: "It is important to note that over the years this group has subjected ordinary citizens using public roads to untold hardship, delays, threats and disruption simply because they insist on using public space irrespective of inconvenience and hardship on other law-abiding citizens and motorists. This cannot be tolerated and must stop."
Road blockades by the IMN during their processions had in the past resulted in clashes with local communities and travellers in many northern states.
A preliminary report by Human Rights Watch stated that Mr El-Zakzaky survived gunshot wounds following the army clampdown that killed over 300 members of the Shiite group.
The IMN, on its part, said over a thousand of its members were killed by the soldiers in the three days between December 12 and 14, 2015, mainly at its headquarters.
A judicial panel of enquiry set up by the Kaduna State Government confirmed 349 deaths - including a soldier. The 348 Shiites were secretly buried in mass graves by soldiers without family members' permission, making it difficult to determine an accurate death toll.
At various times, members of the IMN marched on the streets of Abuja and other cities to protest the detention of Mr El-Zakzaky.
The men, women and sometimes children marched and chanted through the streets, calling for the release of Mr El-Zakzaky and his wife.
Below is the timeline of events that happened since the December 2015 incident.
December 12, 2015: Nigerian Army attacked IMN members who had blocked a public road, killing many of the Shiites.
December 13, 2015: The IMN released a statement saying that Mr El-Zakzaky's son and wife were among the hundreds of Shiites killed.
December 13, 2015: The IMN insisted that its members did not attack the convoy of the Chief of Army staff, as alleged by the Nigerian Army.
December 14, 2015: The army continued the attacks on the Shiites, particularly at the IMN headquarters in Zaria.
December 15, 2015: The army said the Shi'ite leader, Ibrahim El-Zakzaky, and his wife were "safe and in protective custody."
December 18, 2015: President Buhari did not make any public statement on the killings but a presidential spokesperson said that the incident was "a military affair."
December 23, 2015: Human Rights Watch published a report saying over 300 members of the Shiite group were killed.
January 14, 2016: The Islamic Movement released a statement saying its leader, Mr El-Zakzaky, and his wife, Zeenah, were recuperating from gunshot wounds at an undisclosed location in Abuja.
April 5, 2016: Human rights lawyer and counsel to Mr El-Zakzaky, Femi Falana, revealed that Mr El-Zakzaky had become partially blind.
December 2, 2016: A high court ordered the release of El-Zakzaky noting the decision of the government to hold him for so long was dangerous.
Citing the death of former Boko Haram leader, Mohammed Yusuf, in custody, the judge said; "If the applicant dies in custody, which I do not pray for, it could result in many needless deaths."
The judge ruled that the government should within 45 days release the applicant and his family to the police, who shall within 24 hours take them, guarded by escort, to a safe place.
December 14, 2016: A human rights group described the continued detention of Mr El-Zakzaky despite the court ruling as "a hardening of dictatorship behaviour."
January 15, 2017: The 45 days deadline given by the judge elapsed with the Nigerian government failing to release the IMN leader.
January 16, 2017: Amnesty International told the Nigerian government to obey the court and release Mr El-Zakzaky and his wife.
March 9, 2017: The wife of Mr El-Zakzaky, Zeenat, wrote an open letter to President Buhari recalling the events of July 2014, "the month that the Nigerian army under former president Goodluck Jonathan extra-judiciously killed three of my sons among 35 Muslims exercising their constitutional rights of assembly."
May 23, 2017: The federal government said Mr El-Zakzaky was still in detention because there are additional charges against him for which he has not been granted bail.
May 24, 2017: The presidency declared that Mr El-Zakzaky's detention was in the public interest.
November 9, 2017: IMN made a fresh demand for his release on health grounds.
January 13, 2018: The IMN leader made his first public appearance more than two years after he was detained by the Nigerian government.
April 18, 2018: The Kaduna State Government filed an eight-count charge of homicide against Mr El-Zakzaky and his wife over the death of a soldier in the December 2015 incident.
June 21, 2018: The absence of a judge stalled the trial of Mr El-Zakzaky at a Kaduna high court.
October 29, 2018: Clashes erupted between security forces and IMN followers in Abuja.
November 7, 2018: The Kaduna court rejected the bail application filed by the Shiite leader and his wife.
August 5, 2019: The Kaduna State High Court granted the Shiite leader and his wife leave to travel to India for medical treatment.
August 5, 2021: Nigeria's secret police, the SSS, pledged to obey the court order granting Mr El-Zakzaky bail.
August 13, 2019: Mr El-Zakzaky arrived in India for medical treatment.
August 14, 2019: Mr El-Zakzaky alleged that the condition at the Indian hospital he was taken to was worse than where he was detained in Nigeria.
August 16, 2019: He was returned to Nigeria and he alleged that the federal government working with the Indian government frustrated him from getting adequate treatment. Upon his return, he was placed under arrest.
August 28, 2019: The Nigerian government accused Mr El-Zakzaky of being sponsored by Iran to replicate the 1979 Iranian revolution in Nigeria.
February 6, 2020: The court granted Mr El-Zakzaky and his wife access to personal physicians.
February 6, 2020: The court fixed February 24 and 25 for the continuation of his trial.
February 24, 2020: The court ordered prison authorities to allow the couple full access to medical services before taking their plea on April 23.
November 19, 2020: The court adjourned Mr El-Zakzaky's trial to January 25 and 26 for further hearing.
January 23, 2021: Authorities of the Nigerian correctional facility in Kaduna State said they were not aware that the IMN leader and his wife tested positive for COVID-19 as rumoured.
January 26, 2021: The trial of Mr El-Zakzaky, and his wife, Zeenat, was adjourned to March 8 and 9, 2021, for further hearing.
March 8, 2021: The court adjourned to March 31 for the continuation of trial.
Justice Gideon Kurada adjourned the case to allow the prosecution to close its case.
March 31, 2021: Prosecution closed its case, and asked the court to sentence Mr El-Zakzaky.
The judge adjourned the case till May 25, 2021.
July 1, 2021: Kaduna State High court set aside July 28 to rule on the no-case submission filed by the couple.
July 28, 2021: Court frees the couple in a ruling that lasted over eight hours.
The judge upheld the no-case submission filed by Mr El-Zakzaky and his wife.
July 28, 2021: The Shiite group said the judgment of the Kaduna State high court has vindicated its members and is a victory for them.
July 29, 2021: The Kaduna government said it would appeal the ruling, an indication that the cleric and his wife are not yet totally free.