Pakistan's former military ruler Pervez Musharraf appeared before an anti-terrorism court on Saturday after spending the night at police headquarters in Islamabad, officials said.
Musharraf was moved into police custody after being arrested on Friday, an unprecedented move against a former army chief of staff ahead of key elections.
The arrest relates to Musharraf's decision to sack judges when he imposed emergency rule in November 2007, a move that hastened his downfall.
Musharraf was brought to Islamabad court house in a white bullet-proof Land Cruiser by armed police and paramilitary rangers squads.
"General Musharraf has arrived at the court and proceedings have started," a police official told AFP.
Live television footage showed Musharraf getting out of his SUV and being surrounded by dozens of security guards moving in the courthouse.
Lawyers have petitioned Pakistan's top court to try him for treason for imposing emergency law -- which would be punishable by death or life in prison -- but it would have to be the state that initiates any trial.
He also faces charges of conspiracy to murder opposition leader Benazir Bhutto in 2007 and over the death of a rebel leader during a 2006 military operation.
Musharraf's supporters say the arrest order was nothing more than a settling of scores for his dismissal of judges nearly six years ago.
On Thursday, Judge Shaukat Aziz Siddiqui added terrorism to the charges, accusing him of spreading "fear in the society, insecurity amongst the judicial officers, alarm in the lawyers' community and terror throughout Pakistan".
Musharraf seized power in a bloodless coup, which was widely welcomed at the time in Pakistan, but he was forced out and threatened with impeachment in 2008.
The elected prime minister he ousted, Nawaz Sharif, is now the front-runner in the general election campaign.