How far does DNA travel? It’s one thing to recognize that, as a matter of science, it finds its way where it wants, but it’s another thing entirely when the police take the DNA collected from a rape victim, plug it into their DNA crime database and find that the rape victim is now a suspect in a crime. Yet that’s what happened in Frisco.

The police crime lab “attempts to identify crime suspects” by searching a law enforcement database that includes DNA collected from sexual assault victims, District Attorney Chesa Boudin said Monday.

He didn’t identify the database, but said one woman was recently arrested for a felony property crime based on her DNA collected years ago during a domestic violence-involved rape examination.

That DNA collected during a rape examination raises some significant problems. The collection from the victim was predicated on her limited authorization to be used in the resolution of her alleged crime, not to become part of any police crime database. By adding it to the database, the police exceeded the limits of her providing her DNA to the police. Was this an unlawful search and seizure?

Then there’s the matter of rape victims being dissuaded from coming forward, providing DNA evidence, if it ends up in the database and comes back to haunt them.

“Rapes and sexual assault are violent, dehumanizing, and traumatic. I am disturbed that victims who have the courage to undergo an invasive examination to help identify their perpetrators are being treated like criminals rather than supported as crime victims,” Boudin said in a statement. “We should encourage survivors to come forward — not collect evidence to use against them in the future.”

Boudin’s hyperbolic presumptive rhetoric aside, the fact remains that even women who may have reason to fear their DNA could connect them to their own criminal conduct can be raped, and should be able to report the crime to police without the fear that their actions will end up the use to which the DNA is put rather than identifying the person who raped them.

The contrary argument is that the person whose DNA is collected and ends up matching a suspect in a crime doesn’t get a free pass on the crime she committed. If her DNA ends up matching that of a crime suspect, are the police to ignore it, to let one crime go without resolution in favor of another crime?

Boudin, as well as San Francisco Police Chief Bill Scott, have taken the position that evidence collected by rape victims must be protected in order to create no disincentive for victims to come forward.

“We must never create disincentives for crime victims to cooperate with police, and if it’s true that DNA collected from a rape or sexual assault victim has been used by SFPD to identify and apprehend that person as a suspect in another crime, I’m committed to ending the practice,” he said.

Whether this applies to all purported crime victims or only rape victims is unclear. In other instances, there is generally no reason to collect DNA and so it doesn’t “travel” from the lab into the DNA database. But if a rape victim happens also to be the person who committed murder, and the police have access to the evidence necessary to identify the killer and, perhaps, prevent a future murder, should they not use it? After all, if the rape victim isn’t also a criminal, why would inputting her DNA into the crime database serve as a disincentive? Why would it concern her at all?

This argument, of course, is wildly simplistic and grounded in the assumption that a great many reasons exist to be concerned about the potential for false DNA findings. While DNA may be the “gold standard” for identification, it’s hardly fool proof and there is no assurance that a wholly innocent person won’t be mistakenly identified as the perpetrator of a crime. There is very good reason for an innocent person, a rape victim, to object to her DNA being included in a crime database.

Then again, whether this possibility is a serious disincentive for rape victims to come forward or a matter of the trendy narrative is a real question. While Boudin characterizes it as treating rape victims as criminals, there are many other grievances that are far more serious and pressing than DNA findings its way into the police database, from harsh police treatment to thousands of untested rape kits.

But the more significant legal reason is that the police did not obtain the DNA with the person’s authorization for them to use it any way they choose. When a person provides the police with DNA for a specific purpose, to identify the perpetrator of a crime, the police aren’t given carte blanche to use that DNA evidence for any purpose of their choosing, including inputting it into their crime database.

Being the victim of a crime does not compel the forfeiture of Fourth Amendment rights, and there is no rational basis for the police to take advantage of the fact that a rape victim has provided her DNA for one very discrete, very limited, purpose and use it for any other purpose.

Sure, they now have it. Sure, it could be useful to police for other purposes. Sure, the fact that it may serve to identify the perpetrator of another, unrelated crime, is significant to their investigation. But they didn’t come into possession of that evidence for that reason, and they have no greater justification to take evidence they possess for one limited purpose and use it for another beyond that authorization than they do to exceed consent to search for any other purpose.

Suppression of evidence is a difficult issue for many to accept, as it might seem wrong for the police to possess evidence of a crime and not be able to use it. That’s the nature of constitutional rights, to impose limits on government overreach and protect the sanctity of individuals from police excess.

But the collection of DNA from a rape victim in no way implies consent for that DNA to find its way into a police database. It doesn’t mean the cops can’t investigate the secondary crime, or arrest whomever they have probable cause to believe committed it. They just can’t use the rape kit DNA to make the case, anymore than they would have been able to “solve” the case had the victim not been raped and the DNA never been collected.