"In the past we've given India full access to Headley, and I think that when a case is in litigation it's impossible to do that.
"But moving forward, I think we would look for... or consider further access," State Department spokesman Mark Toner said at his daily news conference.
Headley, a Pakistani-American LeT operative, has completed his testimony before a Chicago court conducting the trial of his childhood friend Tahawwur Rana, another key accused in the Mumbai attacks.
Headley has pleaded guilty to 12 terrorism charges related to Mumbai attacks and other plots in the wake of his 2009 arrest in the US.
However, Rana, a Pakistani-Canadian, has maintained that he is not guilty in the charge of "support to terrorism".
During Rana''s trial, Headley testified that he had conducted a surveillance of the German Bakery in Pune and identified Chabad houses in Delhi, Pushkar and Pune as potential bombing targets.