Guatemalan authorities on Tuesday arrested former president Alvaro Colom on corruption charges, along with 10 members of his 2008-2012 government, including the current chairman of scandal-hit Oxfam International.
Colom, 66, was taken into custody at his home in an upmarket district of the capital, the head of the special anti-graft prosecution unit, Juan Francisco Sandoval, said.
Also arrested was Juan Alberto Fuentes Knight, a former finance minister and current chairman of Oxfam International, the British-based charity rocked by accusations of sexual misconduct and exploitation by some staff members in Haiti, Chad and South Sudan.
There was no suggestion of any link between the Guatemala graft accusations and the scandal engulfing Oxfam.
The allegations against Colom and his former ministers related to graft in the public transport system.
The ex-president told reporters as he was brought to the main court building in Guatemala City that he was confident of being exonerated.
"I am certain this will turn out without foundation ... For us, everything is legal," Colom said.
"I am confident that everything we did was correct," he said, speaking calmly and wearing a dark blue suit.
The judge hearing the case said a decision would be announced February 23 as to whether the matter would go to trial.
Colom was in power for four years from 2008. He was succeeded in 2012 by Oscar Perez, who is in jail pending trial over a separate corruption scandal.
Guatemala's current president, Jimmy Morales, was elected in 2015 on his promise to clean up rampant graft in the Central American country. But he too has come under scrutiny for suspected wrongdoing.
Last month, the country's chief prosecutor, Thelma Aldana, said she did not see Morales "as an ally in the fight against corruption."
Morales triggered a public and political backlash last year when he tried to boot out the Colombian head of a UN-backed anti-corruption body that has been instrumental in bringing scrutiny to bear on graft cases in the country.
Colom and the 10 other suspects are accused of fraud and embezzlement in the 2009 purchase of hundreds of buses to ply routes in the capital, Sandoval said.
Four companies were given 25-year government contracts to run the services. The buses were allegedly bought at inflated prices.
The original plan called for purchasing 3,500 buses, but in the end only 400 were delivered, and of those only 50 are running, according to Citizens Action, a Guatemalan group linked to the watchdog Transparency International.
Also in 2009, Colom's party, the center-left National Unity of Hope party, tried to pass a law exempting the transaction from taxes.
Colom and the nine ministers and one deputy minister arrested signed the deal setting up the transport system, baptized TransUrbano.
The former ministers include those who held portfolios for finance, governance, education, defense, labor, health and environment.
Fuentes, who served as Colom's finance minister, was appointed chairman of Oxfam International in April 2015.
An Oxfam spokesperson said: "As far as we are aware, no formal charges have been made against Dr Fuentes Knight. He has been entirely open with the Oxfam board and executive about the investigation which began after he was appointed as Oxfam chair."
Fuentes "maintains his innocence and assures us that he has cooperated fully with the investigation," the spokesperson said.
Revelations that Oxfam staff used prostitutes in Haiti and Chad, as well as new accusations of sexual assault in South Sudan, have put the charity -- partly funded by the British government -- under pressure.
Oxfam deputy chief Penny Lawrence resigned on Monday after the Haiti allegations came to light, saying "I am ashamed that this happened on my watch and I take full responsibility."