His attorney, Karen Friedman Agnifilo, also complained on Friday that double jeopardy was being used as a "weapon" against her client.
The comment came after a brief hearing regarding the scheduling of his state and federal trials in the shooting death of Thompson.
Following a lengthy discussion with prosecutors and defense lawyers, Judge Gregory Carro said the state trial would be on June 8, but could be moved to Sept. 8 if an appeal delays the federal trial.
Agnifilo protested, saying her client was being put in an "untenable" situation and that the defense would not be ready on June 8.
"Mr. Mangione is being put in an untenable situation," Agnifilo said. "This is a tug-of-war between two different prosecution offices."
Despite the defense's assertion that it would not be ready for June 8, as they will be consumed with preparing for the federal trial, Judge Gregory Carro told Agnifilo, "You've done a great job. Be ready June 8."
The state trial was initially set to take place before the federal trial, something that the family of the late UnitedHealthcare CEO Brian Thompson had requested. Jury selection for the federal trial has been set for Sept. 8, which will be followed by opening statements and testimony on Oct. 13, according to Police said the words "delay," "deny" and "depose" were written on Mangione's ammunition, which the AP notes is close to a phrase used to describe how insurers avoid paying claims.
The Associated Press contributed to this report.