Jeffrey D. Allred, Deseret News
A photo of Kailey Vijil is displayed during a candlelight vigil in West Valley City Sunday, July 19, 2015.

WEST VALLEY CITY — A 15-year-old West Valley boy accused of enticing a 12-year-old neighbor out of her house and killing her in a nearby horse pasture was charged Tuesday with aggravated murder.

The first-degree felony was filed in juvenile court, but Salt Lake County District Attorney Sim Gill said he will seek to have the boy certified as an adult "based upon the severity of the charge."

A medical examiner determined that Kailey Vijil was killed by "ligature strangulation." Her body was found "with a shirt wrapped around her neck," charging documents state.

The boy, whom the Deseret News has chosen not to name at this time, is scheduled to make his second appearance in court since the killing on Wednesday afternoon.

The teen knocked on Kailey's door about midnight on Friday morning and first asked her 14-year-old sister if she would help him find his lost cat. When she told him no, he asked Kailey if she would help him and she left with him, according to the charges.

When the older sister told her mother that Kailey had left with the boy, the mother tried calling Kailey on her cellphone but she did not answer, according to the charges. About 90 minutes later, the mother approached two West Valley police officers at a convenience store while looking for her daughter and she told them her daughter was missing.

The officers found Kailey's body in a field near 3600 South and 5200 West just before 3 a.m. by "pinging" her cellphone. West Valley police previously said there was evidence of a struggle at the scene.

Police and neighbors said the boy had attempted to lure other young girls out of their homes prior to Kailey and in one case succeeded, but the girl's mother saw what was happening and called her back into the house before she got very far. The grandmother of one girl who was approached about helping to find a lost cat about 20 minutes before Kailey was approached told investigators about the boy and where he lived, police said.

On Monday, the boy was in court for a brief detention hearing before 3rd District Juvenile Judge Kim Hornak. She told the very young-looking boy, who appeared via video monitor from Salt Lake Juvenile Detention, that she needed to keep him behind bars because of the pending murder charge as well as a "possible sexual assault."

The 15-year-old was not charged Tuesday with any sex crime. Gill said only that he filed the charges that were appropriate at this time. He noted that additional charges could be filed in the future, but declined to say whether he had any plans to do so or whether police had gathered evidence of a sexual assault.

Bail was set at $1 million.

The 15-year-old had previously been referred to juvenile court three times for misdemeanors and infractions. He was arrested for investigation of possession of drug paraphernalia in October of 2014, theft in February and burglary nine days after his theft arrest, according to court records.

He was first placed in Salt Lake Juvenile Detention in February and spent 32 days there, according to court records. The boy was placed in an "observation and assessment facility" on May 26. He spent 44 days there before he was released and placed on probation July 9, about a week before Kailey was killed.

A candlelight vigil for Kailey was held at West Valley City Park Sunday night. A private funeral is expected to be held this week on the Goshute Reservation.

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