CHICAGO: A US national who used his Western appearance to carry out surveillance ahead of the deadly 2008 Mumbai siege will be sentenced on Jan 17, a judge ruled Wednesday.

David Coleman Headley, 52, formally admitted to 12 terror charges in March 2010 after prosecutors agreed not to seek the death penalty or to allow him to be extradited to either India, Pakistan or Denmark to face related charges.

He is expected to be sentenced to life in prison with no chance of parole.

The Mumbai siege, which began on Nov 26, 2008 and lasted nearly three days, saw 166 people killed and was the deadliest militant onslaught on Indian soil since independence.

The United States came under fire in India for reaching the deal with Headley, but prosecutors said it was well worth it given the valuable intelligence he provided in order to save his own skin.

Headley also testified against his childhood friend, Pakistan-born Chicago businessman Tahawwur Hussain Rana, who was convicted on two terrorism charges last year.

Rana, 51, faces up to 30 years in jail for helping the banned militant group Lashkar-i-Taiba (LT) plan an attack on a Danish newspaper that sparked outrage by publishing blasphemous cartoons.

However, a jury found there was insufficient evidence that Rana was involved in the Mumbai attacks — even though Headley described how he had used Rana's immigration services business as a cover while conducting surveillance in India's financial capital. Rana will be sentenced on Jan 15.

The only one of ten heavily-armed gunmen to have survived the three-day siege — Pakistani national Mohammad Ajmal Kasab — was hanged in an Indian prison last week.