Detectives hunting the person who strangled a New York City runner were encouraged after recovering a DNA profile of her probable killer.

A month later, their optimism has waned.

The DNA profile worked up from the genetic material found beneath Karina Vetrano's fingernails and elsewhere doesn't match profiles in state or federal databases.

That means the sample now joins 56,530 others on file with in New York that have been lifted from crime scenes but not linked to a person.

DNA experts say this scenario is not uncommon.

They say that when a DNA profile doesn't hit, investigators must use old-fashioned detective work to solve their case.

Police in New York say they're working around the DNA issue by checking video, interviewing runners and pursuing leads.