NEW DELHI, November 7: Serious trouble is brewing in the Delhi Bharatiya Janata Party (BJP) with the state unit chief Kedar Nath Sahni, accusing Chief Minister Sahib Singh Verma of using a private detective agency for keeping surveillance on his predecessor Madan Lal Khurana.In a letter along with two audio cassettes sent to party president L K Advani, Sahni has also accused the Chief Minister of prompting a CBI probe against Khurana. The CBI however, gave Khurana a clean chit in its ``verification report'' two months ago.According to BJP sources, a number of party MLAs have also complained to the state unit chief that the Chief Minister was using unconstitutional means to keep a watch on their activities.The audio cassette Sahni sent to the party president, carries a conversation between an influential lottery agent and a senior Congress leader who was a union minister. The lottery agent is known for his proximity with Verma. The recorded conversation hints at the hiring of a private detective agency by the said agent to keep a watch on Khurana. The agency was allegedly hired at the time when Khurana had resigned as party vice-president when the high command did not concede his request for returning as Chief Minister following his acquittal in the Jain Hawala case.Some weeks ago, the entire contingent of security personnel detailed for Khurana's security was changed after the former chief minister expressed apprehensions that his political activities were being reported to Verma. Some of the security personnel were detailed with Khurana for as long as five years.Khurana supporters allege that Verma started these activities after the former chief minister's acquittal in the hawala case which was followed by his claim for reinstallation as chief minister. The CBI which had earlier filed a benami complaint of March 19,1996, revived the investigations. It was done at the behest of Verma who had called up the CBI within a week of Khurana's acquittal on May 15,1997. The CBI official, it is claimed, recorded on file that Verma had called up to pursue the complaint against his predecessor.Subsequently, the CBI checked the bank accounts of Khurana, his wife, son, and a senior IAS officer of the UT cadre and investigated the charges levelled in the benami complaint before giving the former chief minister and the IAS officer a clean chit. Verma, when approached for a comment, said :``It is forged and fabricated. I can't believe Sahniji can write such a letter. He is our pradesh president and he should have inquired from me before writing such a letter, if he has written any such letter.''