Robert E. Crimo III arrives in the courtroom at the Lake County Courthouse in Waukegan on Monday morning ahead of opening arguments in his trial where he was charged in the mass shooting that occurred at the Fourth of July parade in Highland Park in 2022. | Photo: Nam Y. Huh/AP (Pool)

Robert Crimo III has pleaded guilty to all charges as opening arguments were set to begin Monday in his trial for killing seven and shooting 48 others at the Highland Park Fourth of July parade.

The trial for Crimo III, 24, of Highwood, entered its fourth day on Monday at the Lake County Courthouse in Waukegan with Lake County Judge Victoria Rossetti presiding.

Crimo III appeared wearing a black suit and his public defender informed the judge that Crimo III wished to change his plea.

Robert E. Crimo III listens to Lake County Judge Victoria Rossetti Monday morning at the Lake County Courthouse in Waukegan as opening arguments in his trial for the Highland Park mass shooting were set to begin before Crimo III changed his plea to guilty in the case. | Photo: Nam Y. Huh/AP (Pool)

Crimo III pleaded guilty to all 69 charges — 21 counts of first-degree murder and 48 counts of attempted murder.

Rossetti asked Crimo III numerous standard questions before accepting his plea, including whether he understood that he was waiving his right to a trial.

The change in plea came following the start of the trial last week, which began last Monday with jury selection. 18 jurors were selected by Wednesday and opening arguments were set to begin today.

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Robert E. Crimo III (left) listens to Lake County Public Defender Gregory Ticsay (right) during his trial for the Highland Park mass shooting where Crimo III changed his plea to guilty in the case on Monday morning. | Photo: Nam Y. Huh/AP (Pool)

Rossetti scheduled a sentencing hearing for April 23. Crimo III faces a mandatory life sentence in prison.

During Monday’s court hearing, the mother of Crimo III interrupted the court as her son was pleading guilty. She claimed he could not plead guilty due to a “federal court order.”

Rossetti had the woman approach the well of the courtroom and warned her she would be removed if she interrupted again.

Lake County Judge Victoria Rossetti asks several questions to Robert E. Crimo III after he informed the court he wished to change his plea to guilty in the Highland Park mass shooting case where opening arguments in the trial were set to begin Monday morning. | Photo: Nam Y. Huh/AP (Pool)

Crimo III was charged in July 2022 with 117 charges — 48 of them were dismissed last week — after opening fire on paradegoers attending the Fourth of July parade near Second Street and Central Avenue in Highland Park on July 4, 2022.

Prosecutors previously said Crimo III admitted to “looking down his sights” of his Smith & Wesson M&P 15 semi-automatic rifle before opening fire on the Highland Park crowd.

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Robert E. Crimo III leaves the courtroom after he pleaded guilty in the Highland Park mass shooting case as opening arguments in the trial were set to begin Monday morning. | Photo: Nam Y. Huh/AP (Pool)

Crimo III told investigators he fired two full 30-round magazines before loading a third 30-round magazine and firing.

Seven people were killed and 48 others were shot. 83 spent shell casings were recovered at the scene.

Crimo III remains held in the Lake County Jail without bond as he awaits sentencing.