SALT LAKE CITY — Investigators believe they know the identity of a person suspected of killing two people on the same date two years apart in the same area.

"We know who it is," Salt Lake County District Attorney Sim Gill said Friday.

But because this person was in another jurisdiction Friday and not in custody in Salt Lake County, Gill said he couldn't comment any more about the double murder case. Additionally, prosecutors asked the court to seal updated court filings.

"While I cannot talk the facts about a sealed document, my answer to your question is that the prosecution effort continues to move forward in a positive direction," Gill said.

On Feb. 9, 2006, Sonia Mejia, 29, was strangled to death inside her Taylorsville apartment at 1167 W. Clubhouse Drive (4000 South). She was six months' pregnant.

On the same date two years later, Feb. 9, 2008, Damiana Castillo, 57, was also strangled inside her apartment near 4000 South and Redwood Road — just a few blocks away from where Mejia was killed.

Prosecutors believe the same person is responsible for both killings, though no arrest has ever been made.

During a press conference in 2009, police did not have answers about motives for the killings or whether there is any significance to the Feb. 9 date or if the dates are merely a coincidence. Investigators said at the time they were looking for a young Hispanic male, possibly in his late teens or early 20s, 5 feet 3 inches tall, weighing 135 to 150 pounds, with short black hair.

In 2010, in what was believed to be a first for a homicide case in Salt Lake County, the district attorney's office filed murder charges against a DNA profile. "John Doe" was charged with two counts of aggravated murder, two counts of aggravated robbery, aggravated burglary and aggravated sexual assault in 3rd District Court.

Court records indicate that the district attorney's office filed amended charging documents on April 5, 2017, and an amended arrest warrant under the case created for John Doe. The documents were filed under seal, which typically suggests the new information contains the name of a specific person.