Judge Dredd

By the 2080s, much of Earth has become an uninhabitable wasteland. While some humans manage to survive in the barren "Cursed Earth", the majority of humanity resides in huge Mega-Cities with populations of tens of millions. To combat crime, the traditional justice system has been replaced by a corps of Judges whose role combines those of police officer, judge, jury, and executioner.
In Mega-City One, Joseph Dredd (Sylvester Stallone), one of the most dedicated "Street Judges", assists rookie Judge Hershey (Diane Lane) in ending a block war. Herman "Fergee" Ferguson (Rob Schneider), a hacker recently released from prison, is caught in the firefight and hides inside a food dispensing robot. Dredd arrests Herman for destruction of property, and sentences him to five years' imprisonment. Rico (Armand Assante), a former Judge, escapes from prison with the help of Judge Griffin (JÃ¼rgen Prochnow). He returns to Mega-City One and reclaims his uniform and "Lawgiver" gun. He also finds and reactivates a decommissioned ABC Warrior combat robot.
A news reporter (Mitch Ryan) critical of Dredd is murdered, and he becomes the chief suspect. Dredd is taken to a trial before a tribunal of Council Judges including Griffin and Chief Justice Fargo (Max von Sydow), his mentor. Dredd is found guilty as his DNA is found on the bullets used to kill the reporter (A feature of the Lawgiver is imprinting the user's DNA on each bullet). To save Dredd, Fargo steps down as Chief Justice and, for his last request, asks the Council to spare Dredd's life. Dredd is sentenced to life imprisonment while Fargo embarks on the "long walk", in which a retiring Judge ventures into the wasteland "to bring law to the lawless". Griffin, who freed Rico to frame Dredd for the murder, becomes Chief Justice and instructs Rico to cause chaos in the city.
Dredd is taken to the Aspen penal colony via airship, where he sits next to Herman. En route, the ship is shot down by the Angel Gang, a family of cannibalistic scavengers. They bring Dredd and Herman back to their cave. A squad of Judges investigate the crashed ship and get to the cave, intent on killing any survivors, not rescuing them. Fargo arrives in time to save Dredd's life, but is mortally wounded by Mean Machine Angel (Chris Adamson). A dying Fargo reveals that Dredd and Rico are the result of the Janus project, an experiment in genetic engineering intended to create the perfect Judge using DNA from Council Judges. Dredd deduces Rico framed him for the reporter's murder, using their identical DNA. Believing Griffin is trying to reactivate the Janus project, Fargo urges Dredd to stop him.
In Mega-City One, Rico terrorizes the city and assassinates Judges in various ways. Griffin uses the situation to convince the Council Judges to unlock the Janus files. He plans to create an army of Judges from his DNA. After the Council Judges unlocks the file, Griffin has them killed. Dredd and Herman sneak back into the city and meet with Hershey, who had also discovered the Janus project by herself. They go to the Statue of Liberty where the Janus laboratories are. They encounter the ABC Warrior, which wounds Herman and captures Dredd and Hershey. Rico uses his own DNA as template for the Janus clones, then commands the ABC Warrior to kill Griffin. Herman, despite his wounds, disables the ABC Warrior as Dredd fights Rico, while Hershey fights his assistant. Rico activates his clones prematurely, but they fail to stop Dredd. Dredd pursues Rico to the top of the Statue of Liberty, and a final struggle sends Rico falling to his death.
Central, the city's controlling supercomputer, has recorded the entire event and broadcasts the information, clearing Dredd's name. The remaining Judges ask him to become the new Chief Justice, but Dredd refuses and remains a street judge.

Question: Who is terrorizing the city?
Answer: Rico