Singh accused the Bharatiya Janata Party and the central government of being behind Mishra in his campaign against Kejriwal, saying it was part of a larger conspiracy to 'finish off the AAP and to 'silenc the opposition.
Jain will also address the Assembly during the one-day special session. A few days ago, he had visited the ACB office and shared evidence related to the Rs 400-crore scam, which allegedly took place during the chief ministership of Sheila Dikshit.
Mishra, suspended from the AAP, promised "another revelation" on May 14.
The AAP, which termed Mishra's allegations as "baseless", suspended him from the party's primary membership at the Political Affairs Committee (PAC) meeting on Monday.
In the letter, Mishra claimed that the way AAP leaders and volunteers were quick to brand Bhardwaj as a BJP worker aroused suspicion that the entire episode was scripted "like the past attacks on you (Kejriwal)".More news: Judges mull Japanese internment in questioning travel ban
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He said Kejriwal has no idea about the incriminating material that he has in his possession. Jain said that Mishra was making allegations against Kejriwal's brother-in-law Surendra Bansal who is 'no more.
"Soon, it was revealed that he was not a BJP worker but a coordinator of Jain's Mohalla Clinic and an AAP worker", Mishra said.
Earlier this morning, Mishra's mother had written a letter to Chief Minister Arvind Kejriwal, accusing him of spreading lies about her son. "Sanjay Singh even did some illegal dealings in Russian Federation". "Whatever other politicians used to do (by filing defamation suits), Kejriwal is doing", the ex-minister said.
Singh claimed Mishra had himself written a letter to ACB in September a year ago, saying that the anti-graft body was trying to implicate the chief minister in the water tanker scam under pressure even when his name was not mentioned in the evidence.
He said, "I had sought details of funding of their foreign trips". Also inform the public about the source of money.