"I have already joined the investigation by replying to two notices under Section 91 Cr.P.C dated April 1, 2020, and April 2, 2020, both issued by your good office," he wrote in the letter.
"Kindly supply me a copy of the FIR registered at PS Crime Branch Rohini, New Delhi and also inform if any new section has been added in the FIR," he added.
"Kindly inform me if any new section has been added in the FIR. I am always ready and willing to cooperate in the investigation," he wrote in the letter on Thursday.
Meanwhile, an FIR was filed against four relatives of Maulana Saad in Saharanpur for ignoring the administration's appeal to declare if they had visited Nizamuddin Markaz in Delhi after March 1.
The Delhi Police had earlier issued notices to the Jamaat chief in connection with the gathering orgsed in Delhi in mid-March.
Hundreds of people, who attended the gathering and then went to different parts of the country, have tested positive for COVID-19.
( With inputs from ANI )