The narco-analysis test to be conducted on the accused in Sohrabuddin Sheikh fake encounter case, including suspended Indian Police Service officer D G Vanzara, has been postponed, Directorate of Forensic Science officials said on Monday.

"It seems that there is some problem in the interpretation of legalities regarding the narco-test. So the test of the two persons (out of the total 13 accused) which was scheduled to start on Monday morning has been postponed for the time being," DFS director J N Vyas told reporters in Gandhinagar.

"Two of the accused were to undergo the test from May 5 to May 9. But at about 2 pm we received a message saying that they will not be coming," Vyas said. Now the criminal investigation department will be given fresh dates for the tests, he added.

He clarified that the narco-analysis test of other accused in the fake encounter case will not be conducted till May 9.

In a reply to a question about who were the two persons out of the 13 accused to undergo narco-analysis test, Vyas said, "I have no idea and I just can't tell who they are. We were intimated that two persons were going to come". However, CID (crime) sources said one of them was Vanzara.

A local Ahmedabad court had earlier given permission to the investigating agency to conduct the narco-analysis tests on the accused in the fake encounter case.

The accused have not challenged the lower court order in the high court.

Three IPS officers -- Vanzara, Rajkumar Pandian and Dinesh M N -- were arrested in the fake encounter case in 2007. Ten other police officers are also behind bars in the same case.

Sheikh was killed on the outskirts of Ahmedabad in November 2005. His wife, Kausar Bi, was also allegedly killed and her body was disposed of subsequently by the accused.