Michigan criminal proceedings may be initiated either through the filing of a complaint and information by the prosecuting attorney or through a grand jury indictment under MCL 767.1 et seq. In People v Glass, 464 Mich 266 (2001), the Michigan Supreme Court confirmed that there is no state constitutional right to indictment by a grand jury and that the grand jury indictment serves as a procedural alternative to the preliminary examination. In either path to prosecution, the investigation phase that precedes formal charging is the period during which the prosecutor and law enforcement gather the evidence they will use to build their case. The quality of a defense attorney's intervention at this stage directly determines the evidentiary landscape at trial.

The primary constitutional tools available to a criminal defense attorney during an investigation are the Fourth Amendment protections against unreasonable searches and seizures, the Fifth Amendment privilege against compelled self-incrimination, and the Sixth Amendment right to counsel. The Fourth Amendment, enforceable against the states through the Fourteenth Amendment, governs search warrants, warrantless arrests, and the admissibility of evidence obtained through unlawful means. Probable cause—defined as "a substantial basis for inferring a fair probability that contraband or evidence of a crime will be found in a particular place," People v Armstrong, ___ Mich ___ (2025)—is the constitutional floor for any search warrant. A warrant that fails this standard, or that fails to describe the place to be searched and items to be seized with the particularity required by MCL 780.654 and People v Collins, 438 Mich 8 (1991), is constitutionally infirm and the evidence obtained under it subject to suppression.

The Fifth Amendment privilege against compelled self-incrimination, applicable to state proceedings through the Fourteenth Amendment, protects a person from being compelled to be a witness against himself in any criminal case. This privilege applies not only at trial but during any investigative proceeding in which the person's testimony could be used against him in a criminal prosecution—including police questioning, grand jury proceedings, and investigative subpoena examinations. The right is self-executing in the sense that it must be affirmatively invoked: silence in the face of investigative questioning, standing alone, does not constitute an invocation. For this reason, having an attorney who knows exactly how and when to invoke the Fifth Amendment is essential.

Michigan's investigative subpoena statute, MCL 767A.2 et seq., authorizes the prosecuting attorney to petition the court to issue investigative subpoenas to investigate the commission of a felony when there is reasonable cause to believe a felony has been committed and that the subpoena target may have relevant knowledge. People v Farquharson, 274 Mich App 268 (2007). Crucially, investigative subpoenas must include a statement that the person may have legal counsel present at all times during questioning under MCL 767A.4(g). A person served with an investigative subpoena who fails to object under the procedures of MCL 767A.6(1) risks a finding that any testimony given was voluntary—making early consultation with defense counsel before any response to the subpoena indispensable.

The Electronic Communications Privacy Act, 18 USC 2510 et seq., governs the government's access to electronic communications and stored records. Law enforcement increasingly relies on electronic surveillance, cell-site location data, and stored digital communications in Michigan criminal investigations. Following Carpenter v United States, 585 US 296 (2018), the United States Supreme Court held that government access to seven days or more of cell-site location information requires a warrant supported by probable cause, rejecting the third-party doctrine as applied to comprehensive digital records. Michigan defense attorneys must now evaluate digital evidence for compliance with Carpenter and its evolving progeny in every case involving electronic investigation.