Livermore National Laboratory/ZUMA Press/NewscomImagine for a moment that, quite out of nowhere, police showed up and accused of you raping someone last Tuesday evening. They even claim to have DNA evidence of your crimes against this person, whom you've never met. How might you go about showcasing your innocence?
Naturally, the first step would be to prove you weren't at the alleged crime scene. If others can vouch for your whereabouts on Tuesday evening, you would give them as alibis. You might offer up receipts from bars visited or taxis taken that night, turn over GPS data from your vehicle, or show evidence of cell phone use—texts, calls, photographs—from this time. Detectives could easily check your word against taxi, ridesharing-service, phone, or bank data, and they might ask around to wherever you drank, dined, waited in line, picked up your kids, or whatever to see if anyone remembers seeing you. Maybe they check surveillance video from your subway stop or a 7-11 you stopped in, or get your apartment building's security footage. Maybe they find a neighbor who saw you pull into your garage, go out back to star gaze, take out your recycling...
The point is that unless you live all alone in the forest, there's a good chance you could establish where you were last Tuesday night, and conjure up enough evidence of it to drive reasonable doubt.
That is, if you're innocent. If you're guilty, all of the above works in the reverse (regardless of whether DNA evidence exists). Everyone who saw you, everywhere you traveled, and everything you paid for could place you at or near the crime scene. And for sexual assault cases, where it often comes down to the word of the accuser against that of the accused, these sorts of details could provide the crucial context needed to get a conviction—especially in cases where an assailant admits to being with the victim but claims the sex was consensual. Catching the accused in a lie about other parts of the evening, finding someone who saw them acting or looking suspicious, checking footage from places visited before or after, etc., might lead to tidbits that could help establish guilt.
Of course, this only holds if the victim comes forward soon after the attack. The key with all these potential ledes is temporal proximity: People's memories from a few days ago are still relatively fresh, security footage is still available, you (the wrongly accused in this scenario) still might still have a relevant bodega or McDonald's receipt lying around. A dorm mate or neighbor may remember seeing the assailant.
But imagine instead that the victim waits three months to file a police report. Some of the above—the nosy neighbor, say, or the pocketed receipts—will likely have been lost (who remembers minute details of some random Tuesday night three months ago?). Give it a bit longer, and more potential clues will have disappeared. Now give it six years, or 16, or 20. By that point it's not just the corroborating or exculpating GPS data, bar comrades, and bank records that are lost. Key witnesses may have died or moved off to unknown places. The bar where staff could alibi you no longer exists. All of this makes it much less likely that a victim will see (long-awaited) justice, that a rapist will be held accountable, and that a person wrongly ensnared will be able to prove their innocence. It's a lose situation all around.
Then there's the question of DNA. Any chance police had of finding useful DNA evidence at the assault location is obviously long gone, but perhaps the victim saw a doctor after the assault and had a medical forensic exam (also known, somewhat unfortunately, as a "rape kit"). This evidence, which would include samples from any semen found plus DNA evidence found anywhere on the victim's body, was sent from the hospital to a state crime lab, where it has been stored in vacuum-sealed bag inside a cardboard box inside a storage freezer for several decades. While DNA evidence does degrade with time, it should still be good for a few centuries—if stored perfectly. Thus far, however, law-enforcement forensics units have been notoriously bad at collecting, storing, and analyzing forensic evidence without making mistakes, and the longer these labs are holding on to a rape kit, the more chance for errors human or environmental. Forensic evidence storage areas in a lot of places are hardly high-tech operations, and policies for handling and keeping such evidence often ad-hoc.
Plus, as Matther Shaer put it in an Atlantic feature last year, "science is only as reliable as the manner in which we use it." And research has shown that the way we interpret DNA is highly subjective. In one 2010 study, researchers obtained documents from a 2002 Georgia rape trial in which two forensic scientists said the defendant could not be excluded as a DNA match for the mixture of sperm found inside the victim (the defendant was found guilty). In the study, the same DNA sample was shown to 17 experienced lab technicians, without context, who were then asked whether the mixture included DNA from the defendant. Twelve concluded that it definitely did not, one concluded that it definitely did, and four said it was inconclusive. "In other words," Shaer writes, "had any one of those 16 scientists been responsible for the original DNA analysis, the rape trial could have played out in a radically different way."
A similar DNA sample, processed long after it was collected and long past the point when corroborating evidence in the case is available, could be a powerful weapon of injustice indeed.
In the past, this hasn't been a big problem. But a host of factors—advances in forensic testing, a culture that's more supportive of rape victims coming forward, states storing rape-kit evidence longer, and a loosening of state statutes of limitations on rape charges—mean we could wind up with a lot more cases where sex crimes that rely on DNA evidence are being prosecuted years or decades after they occur. And if this happens, the results could be bad for assault victims, bad for innocent people, and bad for the concepts of due process and criminal justice as a whole.
But the force is strong with this one at the moment. Since the start of 2017, legislatures in Minnesota, Oklahoma, Oregon, Washington state, and Washington, D.C. have considered bills that would drastically expand or outright end the statute of limitations for pressing charges in sexual assault cases. In late 2016, California Gov. Jerry Brown signed into law a measure removing the state's statute of limitations on rape and other sexual offenses entirely; prosecution was previously limited to 10 years.