Can police legally acquire DNA samples from a private hospital or laboratory without a court order or even probable cause? From a suspect's coffee cup left on a restaurant table? And does the advent of DNA evidence merit the creation of an exception to the statute of limitations for sexual assault?

Ed Imwinkelried, a professor of law at UC Davis and one of the country's leading experts on DNA and other scientific evidence, says the courts and public policy have yet to adequately address these and other major legal issues surrounding the use of DNA evidence.

"If the criminal justice system is to realize the full potential of DNA technology while maintaining its essential fairness, the system must come to grips with these issues in short order," Imwinkelried and co-author David Kaye of Arizona State University wrote in a recently published article.

In the Washington Law Review, the professors discuss the issues surrounding forensic DNA analysis, which compares, for example, the genetic markers found in blood, hair or saliva left at a crime scene with those markers found in a suspect's DNA sample.

Although the Fourth Amendment to the Constitution protects against search and seizure without probable cause, Imwinkelried and Kaye say there are some situations in which police would still be able to secure DNA samples without probable cause.

• Even without the consent of the source of the DNA, police can acquire medical records and DNA samples from private laboratories and hospitals because the Fourth Amendment speaks only to the government's searches and seizures.
  
• Police can examine for fingerprints a suspect's coffee cup left at a restaurant, and the professors say human cells left in public places should be treated in the same way, in part because collecting "abandoned" DNA doesn't involve an invasion of the body or a seizure of the person or the person's property.
  
• A DNA sample can be taken from an arrested person without puncturing the skin, and the Fourth Amendment does not bar its use for other purposes.

Imwinkelried and Kaye question whether DNA linking a suspect to a sexual assault warrants an exception to the statute of limitations. One of the statute's main purposes is to protect against the risk that an accused would not be able to assemble adequate evidence for a defense because too much time has passed since the alleged crime, they say. While DNA testing may eliminate any doubt as to the defendant's identity, a case can raise issues other than identity, and a delay may make it difficult for a defendant to compile evidence on the other issues.

The article also addresses racial profiling of suspects and DNA screening of a community to identify potential suspects by default.