Updated

A Chicago man accused of helping scout out the Indian city of Mumbai before the 2008 terrorist attack that left 166 people dead and plotting to attack a Danish newspaper pleaded not guilty Wednesday to charges that could result in a death sentence.

David Coleman Headley, 49, appeared before U.S. Magistrate Judge Arlander Keys in the bright orange jumpsuit of a federal prisoner and wearing leg irons to prevent him from running. Federal marshals stood behind him.

Keys asked Headley if he understood the charges against him, which include conspiring to bomb public places in India and aiding and abetting the murder of six Americans killed during the November 2008 attack on Mumbai.

He said he did.

Keys ordered Headley, who has been in federal custody since October, to remain behind bars and set another hearing for Feb. 23 before U.S. District Judge Harry Leinenweber. He excused Headley from being at that hearing.

"He knows the seriousness and the gravity of the charges against him," defense attorney John Theis said after the hearing.

Federal prosecutors say Headley, an American citizen formerly named Daood Gilani, attended militant training camps in Pakistan and conspired with members of the Pakistan-based militant group Lashkar-e-Taiba to conduct extensive surveillance on potential targets in Mumbai before the November 2008 terrorist attacks.

They say Headley also planned an attack on Denmark's Jyllands Posten newspaper because it published cartoons depicting the Prophet Muhammad in 2005 that set off protests in parts of the Muslim world. That attack never took place.

If convicted of conspiring to bomb public places in India, Headley could be sentenced to death. But prosecutors have said he has been cooperating with their investigation — a point that could weigh on their decision to seek a death sentence.

Headley's co-defendant, 49-year-old Chicago businessman Tahawwur Hussain Rana, pleaded not guilty on Monday to the charges against him. He could be sentenced to life in prison if convicted of the most serious charges.

Two other men, retired Pakistani military officer Rehman Abdur Hashim Syed and accused terrorist leader Ilyas Kashmiri, also are charged in connection with the planned attack on the newspaper. Their whereabouts are unknown, although the indictment said Kashmiri has been in Pakistan's tribal areas, home to various terrorist groups.