Thanks to some hard-nosed digging by the Inquirer, we have a much clearer picture of the cavalier way the Philadelphia Police Department treated rape cases - and the victims of such crimes - over at least the last five years.

(Remember that time span - it's important.)

The department's Special Victims Unit downgraded literally hundreds of sexual assaults to much lesser crimes, leaving the attacks unsolved - and the victims feeling violated one more time.

While we're concerned about what these disclosures say about past police practices (and we'll give the department and Commissioner John Timoney credit for responding by energetically reinvestigating thousands of cases), they also remind us of another of our recent concerns - advances in the use of DNA evidence in rape cases, particularly ones that go unsolved for long periods.

In the old days, the five-year statute of limitations for most serious crimes (excluding murder, but including rape) was generally considered a good thing. With passage of time, memories clouded, witnesses died or disappeared, physical evidence got lost.

But with recent amazing advances in the science of DNA analysis, one especially powerful, long-lived and incontrovertible form of evidence is now available in many criminal cases, especially rape.

When a perpetrator leaves DNA evidence at a crime scene in the form of blood, semen, saliva, hair or tissue, he's leaving a signature that's virtually unique. Once the lab analysis is done, the results can be stored in a computer until police feel they have a viable suspect.

If the DNA matches, that's powerful evidence that they have the right person, regardless of how long ago the crime was committed.

A bill sponsored by state Sen. Stewart Greenleaf, R-Montgomery County, would extend the statute of limitations for all serious crimes in which DNA evidence is available. It's wending its way through the state Legislature (partly sidetracked by another bill he's sponsoring that would make sure that DNA evidence is considered in murder cases, which we firmly support).

Other states, most notably New York, have moved to close the statute-of-limitations loophole for criminals when it comes to DNA evidence.

Now it's time for Pennsylvania to do the same. ------------- ------------------ --------------------- ------------------ --------------------- ----------------- ----------------- -------------------