A link between DNA from the unsolved killing of Sarah Fox, a Juilliard student, in 2004 and DNA taken from a chain placed at the site of an Occupy Wall Street action in March may be the result of a laboratory error, according to two people briefed on the investigation.

One of the people, who spoke on the condition of anonymity, said it appeared that the DNA recovered from skin cells on the slain woman’s portable compact disc player and from the chain found this year came from a Police Department employee who works with the Office of the Chief Medical Examiner.

Nonetheless, the renewed focus on a DNA link to the Fox case has drawn attention to the way investigators are now using DNA collection for far more than just the most serious of crimes.

The decision by investigators to search for DNA samples on the chain, which was used to hold open a subway entrance gate, illustrates how such collections have become a routine part of a wide range of criminal investigations.