A 15-year-old in Utah was arrested Thursday in the deaths of his two younger brothers, ages 4 and 10, police said.

Authorities are treating the case as a double homicide, NBC affiliate KSL reported.

The victims are said to have suffered injuries "consistent with penetrating knife wounds," Davis County Sheriff Todd Richardson told KSL.

"As a result of our investigation, this morning we have taken the 15-year-old juvenile into custody," Sergeant Susan Poulsen of the Sheriff's Office, adding that prosecutors were expected to formally charge the boy on Monday. "We believe he acted alone."

The boys' mother discovered her 4-year-old son dead on the floor Wednesday afternoon upon returning to her West Point home from a dance recital with her three other children, KSL reported. Police later found the second body.

The 15-year-old, who is not being identified because he is a minor, was found late that night wandering the streets about five miles away. He was taken to a hospital for evaluation and minor injuries, officials said.

According to KSL, the teenager has made headlines before, when he ran away from home in 2011. He was eventually found about four miles away.

Ann Durrwachter, a neighbor whose son attends school with the teenager, told KSL the boy was a "model student."

"From what I understand, he's a model student, from what I've heard. I've never had any complaints about him or his family. I always figured him as model 15-year-old that every mom dreamed of having. He was just carefree almost. He just kind of did his own thing as most boys do."

The boys' father is on active military duty. Four of the couple's children were adopted, including the two victims, The Associated Press reported. The 15-year-old is the couple's biological child.

The gruesome act has left the quiet community in shock.

"West Point is just a quiet area. Not that many people even know it exists," Durrwachter told KSL, adding that the family was kind and loving.

"They were definitely a very positive family," she told KSL. "Sweet, sweet family. Our kids played together. They walked up and down our streets, rode bikes."

The arrest comes amid heightened national attention to violence by children following the high profile stabbing death last month of an 8-year-old California girl, Leila Fowler. Her 12-year-old brother has been charged with second-degree murder in her death.

Reuters contributed to this report

The New York college student who was shot during a home robbery early Friday was killed by police gunfire, officials said at a news conference Saturday.

Nassau Co. Police

Nassau County police on Saturday named 30-year-old Dalton Smith of Hempstead as the man who attempted to rob the off-campus home where Hofstra University junior Andrea Rebello was shot and killed.

According to NBC New York affiliate WNBC, Nassau County Police said Andrea Rebello, 21, was killed by police fire, not by the armed gunman attempting to rob the off-campus house where she lived with her twin sister, Jessica, and several other women.

Police identified Saturday the man allegedly involved in the home robbery as Dalton Smith, 30, of Hempstead.

According to WNBC, Rebello, a Hofstra University student, and Smith were both shot and killed as he was trying to back out of a rear door holding the woman in a headlock and pointing a gun to her head, police said. 

An officer fired eight rounds, seven of which hit the suspect and one that hit Rebello, police said, according to WNBC.

According to a police statement, officers responding to a robbery in progress arrived on scene at 2:30 a.m. to find Smith armed with a gun. Three female victims -- the two sister and a third woman -- and one male victim were held inside the home, according to police. Wearing a ski mask, Smith had forced his way inside the house, according to WNBC.

Smith allowed the third unidentified woman to leave, and she called 911, WNBC reported.

Police say Smith was on parole for robbery in the first degree and had an extensive criminal history that includes assault.

A warrant for his arrest was issued last month for absconding from parole.

The judge who will hear the capital murder case against accused Colorado theater gunman James Holmes said Thursday he will hold a hearing on the constitutionality of Colorado's insanity defense law in death penalty cases.

Arapahoe County District Judge Carlos Samour Jr. ruled that he will consider a defense motion that argues the statute is unconstitutional because it prevents  Holmes from calling his own mental-health experts at sentencing if he refuses to cooperate with court-appointed psychiatrists.

This decision comes just three days after Holmes' lawyers said they wanted to change his not guilty plea to not guilty by reason of insanity.

Holmes appeared in court Monday with a thick, brown beard. He sat wordlessly and stared straight ahead as his attorney, Daniel King, told the judge that the defense has a mental illness diagnosis for the 25-year-old former medical student at University of Colorado-Denver.

Prosecutors said last month that they would seek the death penalty for Holmes.

Earlier in the case, defenders had asked then-presiding Judge William Sylvester to declare Colorado's insanity defense law unconstitutional because it compels a defendant to work with court-appointed psychiatrists, which may violate one's right against self-incrimination. Prosecutors objected to these claims.

But Samour, who was assigned the case last month, ordered both sides to present arguments on the issue at a hearing next week.

Court documents read:

"The Court orders the parties to confer... on the defendant's contention that [the insanity defense law] is unconstitutional to the extent it prevents him from calling any psychiatrist or other expert witness to provide evidence of his mental condition at the sentencing hearing if he fails to cooperate with psychiatrists and other personnel conducting the Court-ordered sanity examination."

Twelve people were killed and 58 wounded on July 20, 2012, at a midnight showing of the movie “The Dark Knight Rises” in the Denver suburb of Aurora. Holmes has been charged with 166 counts of murder, attempted murder, and other offenses in connection with the massacre.

Related:

Accused Aurora theater shooter requests plea change

Image: Steven Soden

A DNA test used by investigators to identify victims of serial killer John Wayne Gacy has helped solve a 41-year-old New Jersey missing persons case, officials announced Tuesday.

Sixteen-year-old Steven Soden went missing on April 3, 1972, but his remains were not identified until 2012, when authorities matched them with a DNA sample from his sister.

Soden's relatives contacted the Cook County Sheriff's Office in 2011 after hearing about Sheriff Thomas Dart's efforts to identify several of Gacy's victims. They believed Soden may be one of them, officials said.

"We always had hopes that we'd somehow find him alive," Steven's brother, Ron Soden, 73, told NBC 4 New York Tuesday from his home in Tacoma, Wash. "In this day and age, it's so much easier to find someone over the Internet."

The teen, who lived at an orphanage, was last seen alive on April 3, 1972, running away with 12-year-old Donald Caldwell, from the Bass River Camp Grounds in Burlington County, N.J., during a group camping trip, officials said. Neither boy was ever seen again.

Soden may have headed to Chicago, where his biological father lived, his relatives suggested — and there he may have come into contact with Gacy.

Tim Boyle / Des Plaines Police Department vi

This is John Wayne Gacy's police arrest photo from Dec. 21, 1978. Following intensive research, investigation and surveillance, Gacy was arrested by the Des Plaines, Ill., Police Department on Thursday, Dec. 21, 1978.

Gacy killed 33 teenage boys and young men in Chicago from 1972 to 1978. He was executed for his crimes in 1994. Seven of his victims remain unidentified.

At Dart's request, a DNA sample was taken from Soden's sister, but there was no match between her and any of the unidentified Gacy victims.

In December 2012, however, her profile matched that of unidentified human skeletal remains found 13 years earlier in New Jersey.

Over the next few months, the Cook County Sheriff’s Office and New Jersey State Police conducted further investigation and obtained additional DNA samples from Soden's half siblings, including a paternal half sibling, to make an accurate identification.

Genetic testing was performed at the University of North Texas Center for Human Identification.

The remains were discovered in the woods in Burlington County in April 2000 — not far from where Soden was last seen.

New Jersey State Police say they're still searching for Caldwell as well as additional evidence in Soden's death, according to Philadelphia NBC affiliate WCAU. His exact cause of death is still unknown.

"You always hope for the best," Ron Soden told NBC 4 New York. "But when you finally get an answer, a partial answer…" He trailed off.

"It's sad," he continued. "The sense of him being so young, and the way it happened, and where it was. He probably ran away because he thought nobody cared about him. It's just not a good story."

In this undated photo released by the Philadelphia District Attorney's office, Dr. Kermit Gosnell is shown.

Former Philadelphia abortion doctor Kermit Gosnell, who was found guilty of first-degree murder, was spared the death sentence Tuesday after he agreed to forgo an appeal.

The Philadelphia District Attorney's Office agreed to two life sentences without the possibility of parole in exchange for not appealing.

Prosecutors had sought the death penalty, but Gosnell's age would have made it unlikely he would be executed before his appeals ran out.

Gosnell, 72, was convicted Monday of three counts of first-degree murder for the death of three babies that prosecutors said were delivered alive and subsequently killed. He was convicted of other charges as well, including infanticide, manslaughter, conspiracy and running a corrupt organization, NBCPhiladelphia.com reported.

The verdict was announced on the 10th day of deliberations, capping a two-month trial that featured grisly testimony about botched late-term abortions and became a flashpoint for both sides in the national abortion debate.

Gosnell was sentenced Tuesday for the deaths of two of the babies. He will be sentenced on the remaining charges, including the death of the third baby, on Wednesday.

Related:

Abortion doctor Kermit Gosnell convicted of first-degree murder