The Attorney General's Office says the man was arrested at his farm in the northeastern municipality of Guarne, about 25 kilometres from Medellin.
Luiz Gonzalez, an official with the prosecutors' office, yesterday identified the man as 44-year-old Jaime Ivan Martinez.
He was being investigated in the disappearance of a 50-year-old woman, Maria Arango, an official from Guarne municipality. She was last seen on Jan 19.
Martinez allegedly confessed to killing Arango and 19 other people and burying them on his farm. Gonzalez said a search for the bodies would be launched soon.