Abhay Thipsay, the special judge hearing the Best Bakery case, has received threatening mails, highly placed sources said on Monday.
The last such mail was received in November, but its content is not known, the sources said. "There are several such mails," they added.
The security for the judge has been beefed up.
Meanwhile, Arthur Road Jail Superintendent Swati Sathe has been asked to appear before the court in connection with the case.
This follows reports about the alleged threat to the life of 17 accused currently lodged in the jail.
Media reports had said that underworld gangster Dawood Ibrahim had planned to kill the 17 to avenge the killings in the Best Bakery incident two years ago.
The reports said a 1993 Mumbai blast accused belonging to the Dawood gang lodged in the prison had planned to poison their food. However, the plan was foiled and the accused were moved to a high-security zone.
According to DIG (Prisons) Rashmi Shukla, the 17 are safe and kept in a barrack that is separate from the cells of other inmates.