Washington (CNN) -- A U.S. citizen has been charged with alleged involvement in planning last year's terrorist attacks in Mumbai, India, the Justice Department said Monday.
David Headley of Chicago, Illinois, already faced charges alleging that he planned attacks against a Danish newspaper.
Headley, 49, was born in Washington, D.C.
The Justice Department alleges he helped plan the November 2008 terrorist attacks in Mumbai, which killed 160 people, including six Americans.
The Justice Department said Headley attended terrorism training camps in Pakistan and conspired with members of the group Lashkar-e-Tayyiba to carry out attacks in Denmark and India.
The United States considers Lashkar-e-Tayyiba a foreign terrorist organization.
The department said Headley was charged in Chicago with six counts of conspiracy to bomb locations in India and to murder and maim persons in India and Denmark, and six counts of aiding and abetting the murder of U.S. citizens in India.
He has agreed to cooperate with authorities investigating both terror plots, lawyers involved in the case said.
At the time of his October 3 arrest in Chicago, he was on his way back to India to plan a second attack, a source close to the investigation said.
He remains in federal custody, with no date set for his arraignment, the Justice Department said.
Headley's attorney, John T. Theis, said he has read the additional charges but said he would not comment "while we have the case under review." No formal plea has been offered to either these charges or the previous ones, he said.
Asked whether his client is cooperating, Theis said, "At this time, we will only say I don't disagree with the statements made by the U.S. attorney regarding my client's involvement in the investigation."
A retired major in the Pakistani military, Abdur Rehman Hashim Syed, also was charged with conspiracy in planning to attack the newspaper in Denmark. So was Tahawwur Hussain Rana, whom U.S. authorities identify as a Pakistani native and Canadian citizen who lives mainly in Chicago.
Headley said he worked for First World Immigration Services, a company owned by Rana, though authorities have said in court papers that surveillance showed that he "performs few services" for the company.
Kia Scherr -- whose husband, Alan, and 13-year-old daughter, Naomi, were killed in the Mumbai attacks -- welcomed the developments in the case.
"Though my loss still causes me much grief, I am grateful for the support of the FBI, who called me personally and informed me of the news," she said. "My hope is that Headley cooperates fully and discloses all information to aid in the investigation ..."
CNN's Drew Griffin and Terry Frieden contributed to this report.