The Congress Tuesday demanded the resignation of Gujarat Chief Minister Narendra Modi till the investigation is over in the 2006 killing of a witness in the Sohrabuddin Sheikh case.

Tulsiram Prajapati was killed in an alleged staged shootout Dec 28, 2006, in which then minister of state for home Amit Shah is the main accused.

Prajapati was the only witness to the December 2005 police shootout in which Sohrabuddin Sheikh and his wife Kauserbi were killed.

"How can he stay as chief minister when the investigation process is going on. The senior leader of Bharatiya Janata Party, Narendra Modi, used his chair and intervened with the justice system," Congress general secretary Ajay Maken said at a press conference.

"There should be an inquiry into it and the Central Bureau of Investigation (CBI) should enquire about it," Maken said.

The issue came to light after a petition was filed by a journalist on the basis of a sting operation done by him.

He alleged that attempts were made by BJP MPs Prakash Javdekar and Bhupendra Singh Yadav to impede the trial and other judicial proceedings by manipulating the complainant with the sole intent to protect Shah.