Lawyer Maria Mitousis lost a hand and suffered other serious injuries in the July 3 blast.
In the following days police discovered other explosive devices at two other law firms.
Police say during the investigation officers searched a home and seized a rifle and ammunition.
Guido Amsel, who is 49, now faces additional charges including a third count of attempted murder, possession of a weapon for dangerous purpose and explosive-related offences.
Police allege that Amsel was targeting his ex-wife and the lawyers who were involved in a lengthy legal dispute between them.