If the state deports a key witness in your trial, your case could be dismissed. Two cases, People v Torres and People v Roldan, outline when this might happen.
In December 2006, the state charged Juan Roldan with the shooting of Saba Barrera. Roldan allegedly shot Barrera three times due to Barrera’s affiliation with a rival gang. In addition to this charge, the state also charged Roldan with the murder of two more rival gang members. In the time between Roldan’s arrest and the trial, the police also arrested Barrera for his gang affiliation, and he was later taken into custody by Immigration and Customs Enforcement (ICE). While Barrera was in a federal immigration hold, the prosecution collected his testimony at a preliminary hearing. After the preliminary hearing, Barrera was deported and was not able to testify at Roldan’s trial. The prosecution still used Roldan’s preliminary hearing testimony at the trial. Barrera’s testimony was the strongest piece of evidence at the trial. Without it, the jury may not have found Roldan guilty and he would not have been sentenced to life in prison without parole.
Roldan appealed his guilty verdict by challenging the fairness of the trial. As Barrera, the key witness for the prosecution, was not at the trial, Roldan’s defense attorney could not cross-exam the statements made by Barrera. The prosecution didn’t attempt to delay Barrera’s deportation thinking they could just use the prior testimony from the preliminary hearing. The failure to do anything to stop deportation of the key witness against him violated Roldan’s Constitutional Right to Confrontation, the ability to challenge any witness’ testimony. As a result, the Court of Appeals of California overturned Roldan’s conviction and granted him a new trial.