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Tuesday marks the anniversary of the strangling of two Salt Lake County women police say were killed by the same man two years apart.

Sonia Mejia, 29, who was six months pregnant, was murdered Feb. 9, 2006, at her Taylorsville apartment. Damiana Castillo, 57, was slain Feb. 9, 2008, at her West Valley City apartment, about a mile from Mejia's.

Police do not know the name of their killer -- but prosecutors on Monday used a DNA profile developed from evidence found at both crime scenes to charge him. Referring to the killer as "John Doe," prosecutors filed documents in 3rd District Court charging him with two counts of aggravated murder, which carry the potential for the death penalty, for the slaying of Mejia and her unborn son.

The killer is also charged with two counts of aggravated robbery, one count of aggravated burglary and one count of aggravated sexual assault, all first-degree felonies punishable by up to life in prison.

Taylorsville Detective Shannon Bennett said the charges were filed now because time limits on filing the charges were about to expire on all but the homicide counts.

Meanwhile, police in West Valley City and Taylorsville ran extra patrols Tuesday. West Valley City police Sgt. Bob Bobrowski said his department mounted "a special operation with about 40 extra people throughout the day going through apartment complexes."

Last year, West Valley City and Taylorsville formed a task force to more efficiently investigate the homicides. But Bobrowski said Tuesday that police have no leads in the cases. "We are hoping for a DNA match," he said.

A match would most likely occur if the killer was convicted and tested in an unrelated criminal case and his DNA profile stored in a national database.

According to initial police reports, Mejia was last seen alive the morning of Feb. 9, when she took her 8-year-old son to school. A man police have described as Mejia's common-law husband came home about 6 p.m. to find her dead in the bedroom of their apartment at 1167 W. Clubhouse Drive (3390 South).

Charging documents filed Monday revealed that a witness observed a Hispanic man holding a bottle of Coke and a bag of chips leaning against Mejia's door and talking with her. The witness told police the man hit Mejia on the side of the head, pushed her into the apartment and kicked the door shut, charges state.

Mejia's husband later found a bag of Cheetos snacks and a bottle of Coke inside the front doorway, charges state.

The husband found Mejia partially nude on the bed with a dark blue bandana around her mouth and a wire around her neck. There was an orange substance consistent with the color of Cheetos on Mejia's right breast, charges state.

The husband told police that neither the bandana nor the ligature belonged to him or Mejia.

Missing were Mejia's keys and her gray 1998 Ford Escort, which was found five days later in a motel parking lot about 12 blocks from her home.

Police believe the killer also stole three pieces of jewelry: a heart-shaped ruby ring, a diamond ring and a medallion of Our Lady of Guadalupe fastened to a gold necklace.

Early on, police ruled out family members in the slaying by analyzing fingerprints and DNA evidence. They said at the time they believed Mejia was killed by a psychopath who had no prior criminal record.

Castillo, who lived at 4000 S. Redwood Road (1700 West), was found by her son, who went to her home after she failed to show up at church on Feb. 10.

West Valley City police Sgt. Mike Powell said Tuesday there are "similarities" between the two cases, but he declined to release additional details about Castillo's slaying.

Powell also declined to discuss an updated FBI profile of the unknown killer. In 2006, Taylorsville police said the FBI advised looking for a person with a history of abusing animals.

Suspect in killings seen by witness

A man seen talking to murder victim Sonia Mejia on the day she died, Feb. 9. 2006, was described as Hispanic in his mid-20s, about 5-foot-6, medium build and short, dark hair combed back. He was wearing denim shorts that hung below the knees, white tennis shoes, no socks and a white T-shirt.