The young and at the time three-star general Mahamat Idriss Deby was proclaimed president by the army two and a half years ago after the death of his father, who led the semi-desert state for more than 30 years.
Now, a referendum on a new constitution is scheduled in two months' time and is due to set the stage for "free" elections and a return to civilian rule.
Deby had said elections would be held within 18 months of his takeover. But last October 20, he pushed that back two more years.
Chadians poured out onto the streets in protest.
Many of the thousands who demonstrated set off from the headquarters of The Transformers, the leading opposition party, in N'Djamena's Abena district.
The junta has admitted that at least 50 protesters died in the capital, while the opposition and NGO's said the true figure from police and army gunfire was far higher.
Hundreds of youth and opposition figures were arrested, although some managed to flee abroad, including Transformers' leader Succes Masra.
- 'Fear in our hearts' -
On October 8 this year, 72 young activists were arrested at the party headquarters and were since detained at a secret location.
"We, the demonstrators from October 20, we are living with the fear in our hearts of being arrested or kidnapped," said Djimrangar Ngueto, who runs an association for the victims of "Black Thursday."
Ngueto is one of very few people still prepared to talk to the media, in the hope that his status as a spokesman will protect him.
He said he was among the people that were arrested on October 20 and released six months later after President Deby spoke of "holding out a hand."
"Nothing has changed for a year, the rulers have even clenched the hand they claimed to be holding out," Ngueto said.
Any rally or demonstration has been systematically banned.
"All that is done in the expectation of trouble before, during and after the referendum," said Evariste Ngarlem Tolde, a political scientist at the University of N'Djamena.
"The army is divided, with one part (of it) in the opposition," he added.
The all-powerful presidential guard "will not hesitate to open fire, and there is a risk that a part of the army confronts it if there are a lot dead," Tolde said.
- Dozens disappeared -
After Black Thursday, the regime said 621 youths, including 83 minors were detained at an infamous desert jail at Koro Toro, 600 kilometers (370 miles) from the capital.
Six weeks later, they were tried in a closed court without legal representation. Many were sentenced to jail.
Local and international NGO's as well as UN-mandated experts estimate that 1,000-2,000 were arrested. Dozens if not hundreds of them have since disappeared.
"We are still asking for their bodies that are hidden in the desert," said Djimrangar Ngueto.
The Human Rights Watch, HRW, said the October 8 arrest of 72 opposition supporters is an attempt to limit political dissent in the country.
The New-York based organization also said an arrest warrant for Transformers' Masra was posted on social media by authorities on October 5.
The warrant, issued in June, appeared after Masra said he intended to return to N'Djamena on October 18. He has since delayed to November.
Masra is wanted for a variety of alleged crimes, from an attempted attack on constitutional order to incitement to hatred and insurrectional uprising.
"Threatening an opposition leader with arrest and detaining his supporters makes clear that fundamental freedoms are still very much at risk," said Lewis Mudge, HRW's Central Africa director.
A government spokesman did not respond to an AFP request for comment on the allegations.
The main reason for the latest arrests "is that Succes Masra ... frightens President Deby and other actors in the transition who have their sights on the next presidential" elections, said Kelma Manatouma, a political science researcher at Paris Nanterre University.