Raymond Allen Davis has been in jail since Jan. 27 on suspicion of murder.
Officials said Davis was charged with murder Wednesday but he was let go after the families of the two Pakistanis he killed pardoned him in exchange for compensation.
A lawyer for the families said the United States paid $2.34 million in "blood money" to secure the man's release.
Davis said he killed the two Pakistanis in self-defense.
The Associated Press contributed to this report.