In 2013, the U.S. Supreme Court upheld a Maryland law authorizing law enforcement authorities to take DNA samples from suspects arrested for serious offenses. Most states have equivalent laws, which treat cheek swabs similarly to fingerprints. (Maryland v. King, 133 S. Ct. 1958 (2013).) (All 50 have laws requiring collection of DNA from defendants convicted of felonies.)
The Maryland statute applies to arrests on charges of violent crimes and burglary offenses. It prevents authorities from processing samples or placing them in databases before arraignment, at which point the court determines whether there is probable cause for an arrest. On the off chance that a judicial officer finds that there isn’t probable cause, the authorities have to immediately destroy the sample. The law also requires them to destroy it if:
- the defendant isn’t ultimately convicted
- the conviction is reversed, or
- the defendant is pardoned.
The DNA officers collect can be used only for identification purposes—for example, to determine whether the defendant’s DNA was found at the crime scene. They can't allow it to be used for other reasons, such as to match family members.
Privacy advocates in states like California have brought challenges to similar DNA-collection laws on the basis that they don’t contain the same protections as the Maryland statute. For example, in Haskell v. Harris, 727 F.3d 916 (9th Cir. 2013), the ACLU argued that California’s law violates the Fourth Amendment, in part because it allows for the collection and preservation of DNA samples of those who are charged with less serious offenses and who aren’t ultimately determined to be guilty.
In fact, in late 2014, a California court determined that the state DNA-sample law violated the state constitution. (For the court's rationale, see California Court: Police Can’t Take DNA From Arrestees.)
Regardless of the exact procedures involved, collecting the DNA of certain kinds of arrestees isn't inherently unlawful. The U.S. Supreme Court has said as much. But, as the California court showed, there may be circumstances in which the collection process violates the law.