Mr Colom, 66, was president of Guatemala from 2008 to 2012.
The chairman of under-fire British charity group Oxfam International, Juan Alberto Fuentes Knight, was arrested Tuesday in his native Guatemala in a swoop related to government graft allegations, officials said. He was recently named by the Organization of American States as an envoy to Honduras in a bid to help sort out a highly disputed election there.
Ex-Finance Minister Alberto Fuentes Knight is the Oxfam chairman.
Guatemalan prosecutors also announced that former Guatemalan President Alvaro Colom has also been arrested as part of their probe into the acquisition of public buses used in Guatemala City, according to The Guardian.
Colom and the other suspects are accused of fraud and embezzlement in the 2009 purchase of hundreds of buses to ply routes in the capital, Sandoval said.
Mr Sandoval said the detentions included the ex-interior minister and the former ministers of finance, defence, economy, education, labour, environment, health and sports and culture.
Winnie Byanyima, the charity's executive director, told the BBC that Fuentes had been "entirely open with his Oxfam board".
Mr. Fuentes Knight said before Tuesday's hearing that he had warned against continuing government payments to the bus companies, citing "anomalies". Four companies signed 25-year government contracts to operate the TransUrbano transport system, a transaction Colom's National Unity of Hope party tried to exempt from taxes. The United Nations anti-corruption mission in Guatemala participated in the investigation.
Mr Colom is the second former president to be investigated over corruption by CICIG in the past months.
They include a customs fraud scandal that allegedly sent kickbacks to then-President Otto Perez Molina and Vice President Roxana Baldetti, leading both to resign in 2015.
Alfonso Portillo, Guatemala's president in 2000-2004, was extradited to the United States and pleaded guilty to money-laundering conspiracy in 2014.