When a woman reports a rape, her body is a crime scene. She is typically asked to undress over a large sheet of white paper to collect hairs or fibers, and then her body is examined with an ultraviolet light, photographed and thoroughly swabbed for the rapist’s DNA.

It’s a grueling and invasive process that can last four to six hours and produces a “rape kit” — which, it turns out, often sits around for months or years, unopened and untested.

Stunningly often, the rape kit isn’t tested at all because it’s not deemed a priority. If it is tested, this happens at such a lackadaisical pace that it may be a year or more before there are results (if expedited, results are technically possible in a week).

So while we have breakthrough DNA technologies to find culprits and exculpate innocent suspects, we aren’t using them properly — and those who work in this field believe the reason is an underlying doubt about the seriousness of some rape cases. In short, this isn’t justice; it’s indifference.

Solomon Moore, a colleague of mine at The Times, last year wrote about a 43-year-old legal secretary who was raped repeatedly in her home in Los Angeles as her son slept in another room. The attacker forced the woman to clean herself in an attempt to destroy the evidence.

Tim Marcia, the detective on the case, thought this meant that the perpetrator was a habitual offender who would strike again. Mr. Marcia rushed the rape kit to the crime lab but was told to expect a delay of more than one year.

So Mr. Marcia personally drove the kit 350 miles to deliver it to the state lab in Sacramento. Even there, the backlog resulted in a four-month delay — but then it produced a “cold hit,” a match in a database of the DNA of previous offenders.

Yet in the months while the rape kit sat on a shelf, the suspect had allegedly struck twice more. Police said he broke into the homes of a pregnant woman and a 17-year-old girl, sexually assaulting each of them.

“The criminal justice system is still ill equipped to deal with rape and not that good at moving rape cases forward,” notes Sarah Tofte, who just wrote a devastating report for Human Rights Watch about the rape-kit backlog. The report found that in Los Angeles County, there were at last count 12,669 rape kits sitting in police storage facilities. More than 450 of these kits had sat around for more than 10 years, and in many cases, the statute of limitations had expired.

There are no good national figures, and one measure of the indifference is that no one even bothers to count the number of rape kits sitting around untested.

Why don’t police departments treat rape kits with urgency? One reason is probably expense — each kit can cost up to $1,500 to test — but there also seems to be a broad distaste for rape cases as murky, ambiguous and difficult to prosecute, particularly when they involve (as they often do) alcohol or acquaintance rape.

“They talk about the victims’ credibility in a way that they don’t talk about the credibility of victims of other crimes,” Ms. Tofte said.

Charlie Beck, a deputy police chief of Los Angeles, said that there was no excuse for the failure to test rape kits, but he noted that integrating a new technology into police work is complex and involves a learning curve. Since Human Rights Watch began its investigation, he said, the department had resolved to test rape kits routinely — and as a result, cold hits have doubled.

While the backlog and desultory handling of rape kits are nationwide problems, there is one shining exception: New York City has made a concerted effort over the last decade to test every kit that comes in. The result has been at least 2,000 cold hits in rape cases, and the arrest rate for reported cases of rape in New York City rose from 40 percent to 70 percent, according to Human Rights Watch.

Some Americans used to argue that it was impossible to rape an unwilling woman. Few people say that today, or say publicly that a woman “asked for it” if she wore a short skirt. But the refusal to test rape kits seems a throwback to the same antediluvian skepticism about rape as a traumatic crime.

“If you’ve got stacks of physical evidence of a crime, and you’re not doing everything you can with the evidence, then you must be making a decision that this isn’t a very serious crime,” notes Polly Poskin, executive director of the Illinois Coalition Against Sexual Assault.

It’s what we might expect in Afghanistan, not in the United States.