Judge Carroll is called in by Jasper Jacks to prosecute Sonny Corinthos for the murder of his wife, Claudia Zacchara. After sitting through the courtroom "theatrics," he declares Sonny free on bail. Meanwhile, Jason, Carly, and Sonny arrange for Michael, the actual murderer, to be sent to the island.
Federal prosecutor Claire Walsh summons Claudia's brother, Johnny Zacchara, to testify. Chaos erupts when Johnny claims Sonny abused his sister. Court is dismissed and the judge reprimands both Diane and Claire. After Johnny is recalled and dismissed again, Robin is called to testify. She tries to paint Sonny in a good light, but is forced to admit that Sonny demeaned Claudia and swore that it would be the last time she ever lied.
Claire informs the judge that they need Maxie Jones' testimony to proceed, but Diane says she cannot testify as she is in the hospital. Maxie tries to get out of it by appearing sicker than she really is, but to no avail. Maxie testifies that she witnessed Sonny get out of Michael's car with a bloody handprint on his shirt. When asked if Michael was in the car, she swears under oath that she couldn't tell.
While Olivia testifies that she doesn't know where Michael was on the night of Claudia's murder, Ronnie tries to locate Michael. He tells Claire that he can't find him. She tells him that they will have to find someone else, and she decides that Sonny's other son, Morgan Corinthos, will work.
Ronnie takes him out of school and brings him to the courthouse to testify. When Morgan gives his testimony, his older brother, Dante Falconeri, comes in and demands the judge let Morgan leave, particularly because Claire had Morgan pulled out of school without Carly's knowledge. Judge Carroll has Dante placed under arrest for contempt of court and allows Morgan to go home with his mother. After going through proper procedure, Morgan is recalled and Dante advises him to simply tell the truth. Morgan returns home upset thinking that he will be the reason Sonny is sent to prison. Carly tells her son that Claire will be out of a job soon enough.
Carly is called to the stand and shows up in court with Josslyn. Claire objects, saying Carly is trying to sway the jury, but Carly says that her nanny wasn't available. The judge orders a recess, and Carly comes back without Josslyn and swears that Sonny killed Claudia on accident and that it was justifiable homicide, which only further weakens Claire's case against Sonny.
A few weeks later, Alice is about to announce the jury's verdict, but Dante comes in and tells the judge that Sonny didn't kill Claudia- Michael did. The jury is ordered back to their room and to dismiss Dante's outburst. After hearing Dante out, the judge orders a warrant for Michael so he can question him. Carly is called back up to the stand since she perjured herself earlier, but she maintains that Sonny killed Claudia and Michael walked in afterwards. After Michael is found at the Quartermaine boathouse, he is taken to court and questioned by the judge. He recounts the night's events and Judge Carroll thanks him for his cooperation. He remands Michael into custody to await sentencing on Friday with no bail. Dante leads Michael away and the judge tells Sonny that he is free to go, but charges could still be brought against him for the cover-up.
On Friday, the day of Michael's sentencing, Johnny testifies that Claudia would not want Michael to pay for her murder. The judge thanks him and then sentences Michael to five years in prison with the possibility of parole in two. He comments that everyone in the courtroom should be punished for their acts, but watching Michael go to prison will have to be punishment enough. Everyone is taken aback by the unfair ruling, and Dante and Claire are hit the hardest; Dante had believed all along that Judge Carroll would see Sonny as detrimental to Michael's well-being and pass a lenient sentence on him, and Claire had always believed that Sonny was Claudia's killer and never expected that it was Michael. Johnny rails at Dante and blames him for protecting Sonny once again and sending Michael to prison. Outside the courtroom, Morgan, Kristina, and Molly rail at Dante and blame him for sending Michael to prison as well, with Morgan calling Dante a liar and wishing he was dead, Kristina blaming him for using everyone to hurt Michael, and Molly railing about how cops are supposed to help people instead of sending them to prison.
Judge Carroll goes over to the police station on May 14 and Dante and Lucky try to get him to rethink Michael's sentencing, but he tells them his ruling is final. After he leaves, Lucky suggests they find something to blackmail him with. They enlist Lulu and Jax's help, but they are unable to come up with anything. Lucky asks Dante how desperate he is, but Dante refuses to fabricate evidence.
In mid-June, Dante visits Judge Carroll in his chambers and requests that Michael be released. The judge says he will allow Michael to be released from prison under certain conditions. Michael has to live with Dante, wear an ankle monitor, and have minimal contact with Sonny. Dante agrees on Michael's behalf.
The judge visits Johnny in jail and Johnny insists that Sonny framed him. Johnny warns him not to trust Claire because she is getting close to Sonny. He tells him he will launch an investigation on her.
Though he has yet to make any further appearances on-screen, Judge Carroll has had further influence off-screen. On November 17, 2010, he approves of a petition set by Claire to allow Sonny and Michael contact with one another whenever they want to see each other, and on June 15, 2011, he agrees to let Michael off parole two months early after hearing from Dante that Michael has made a lot of progress and that he has just graduated from high school.