(CNN) Here is a look at missing children in the United States. There are several different types of missing children: runaways, family abductions, lost or "thrown away" and non-family abductions. Advances in technology, communications through public alerts and greater cooperation from law enforcement have facilitated the recovery process.

Statistics

AMBER Alert

The AMBER Alert system began in 1996 and was named in honor of Amber Hagerman, a 9-year-old who was abducted in Arlington, Texas, and murdered.

All 50 states, the District of Columbia, Puerto Rico, and the US Virgin Islands have AMBER Alert plans in place to help find missing children in danger.

As of February 2020, the AMBER Alert program has been credited with the safe recovery of 985 children.

Notable and Recent Cases

This list represents selected notable and/or recent cases.

Carlie Brucia

February 1, 2004 - 11-year-old Carlie Brucia is kidnapped on her way home from school in Sarasota, Florida. The abduction is captured on surveillance video at a car wash.

February 6, 2004 - Brucia's body is found.

February 20, 2004 - Mechanic Joseph P. Smith is indicted on charges of first degree murder, kidnapping and sexual battery.

November 17, 2005 - Smith is found guilty.

December 1, 2005 - A jury recommends the death penalty for Smith by a 10-2 vote.

March 15, 2006 - Judge Andrew Owens formally sentences Smith to death.

July 2017 - Sarasota County Circuit Judge Charles Roberts vacates Smith's sentence and orders a new sentencing trial, following the Florida Supreme Court's 2016 ruling that jury recommendations must be unanimous in order to impose a death sentence.

April 2018 - The Florida Supreme Court orders resentencing for Smith in a 4-3 decision.

April 21, 2020 - A judge reinstates Smith's original sentence of death, citing a Florida Supreme Court reversal in January that jury recommendations do not need to be unanimous in order to impose a death sentence.

Dylan and Shasta Groene

May 16, 2005 - 9-year-old Dylan and 8-year-old Shasta are reported missing from their home after their mother, her boyfriend, and their older brother are found murdered in their Coeur d'Alene, Idaho, home.

July 2, 2005 - Shasta is rescued at a Denny's restaurant with her captor, Joseph Edward Duncan III, a convicted sex offender. Duncan is arrested for Shasta and Dylan's kidnapping.

July 10, 2005 - Remains found at a Montana campsite are identified as Dylan's.

July 12, 2005 - Duncan is charged with three counts of first degree murder.

October 16, 2006 - Duncan pleads guilty to murder and kidnapping and is sentenced to life without parole for the kidnappings. He is still eligible for the death penalty for the three murders.

2008 - Duncan receives three death sentences and six life terms in federal and state courts.

Amber Hagerman

January 13, 1996 - 9-year-old Amber Hagerman is abducted as she rides her bike in a parking lot near the home of her grandparents in Arlington, Texas.

January 17, 1996 - Hagerman's body is found near a creek about eight miles from where she was abducted.

Her killer is never found and the case remains unsolved. Her abduction and murder led to the creation of the AMBER Alert system.

Laura Hobbs and Krystal Tobias

May 8, 2005 - Laura Hobbs and Krystal Tobias are reported missing from their homes in Zion, Illinois.

May 9, 2005 - Laura's father, Jerry Hobbs, discovers Laura and Krystal's stabbed and beaten bodies in a neighborhood park.

May 10, 2005 - Jerry Hobbs is arrested and charged with the murders.

August 4, 2010 - The murder charges are dropped and Hobbs is released from prison after DNA links the killings to Jorge Torrez, a man jailed in Virginia.

December 2010 - Torrez is given five consecutive life sentences in Virginia for kidnapping and rape.

Shawn Hornbeck

October 2002 - 11-year-old Shawn Hornbeck is kidnapped while riding his bicycle to a friend's house near his home in Richwoods, Missouri.

January 2007 - The police find Hornbeck and another missing boy, 13-year-old Ben Ownby, who had been held for four days, in the Kirkwood, Missouri, apartment of Michael J. Devlin.

December 21, 2007 - Devlin receives 74 life sentences.

Lisa Irwin

October 4, 2011 - 10-month old Lisa is found to be missing from her crib by her father, Jeremy Irwin, when he returns home from work between 3 a.m. and 4 a.m. in Kansas City. Also missing are the family cell phones.

November 23, 2011 - The command post investigating Lisa's disappearance is shut down. FBI and Kansas City police had been involved; Kansas City detectives remain on the case.

Megan Kanka

July 29, 1994 - 7-year-old Megan Kanka is lured by Jesse Timmendequas, a neighbor and convicted sex offender, into his house across the street from her own house in Hamilton Township, New Jersey, where he sexually assaults and strangles her. Her body is found in a park the next day.

1997 - Timmendequas is convicted and sentenced to death.

Kanka's death inspires Megan's Law, which requires that convicted sex offenders register with local police and the community be notified of their presence.

Polly Klaas

October 1, 1993 - 12-year-old Polly Klaas is abducted during a slumber party at her home in Petaluma, California.

November 30, 1993 - Richard Allen Davis is arrested, and days later he confesses and leads police to Klaas' body.

June 1996 - Davis is convicted and sentenced to death for her abduction and murder.

Klaas' kidnapping prompts California to pass the "three-strikes" law, which gives a life term to those convicted of their third felony.

Jessica Lunsford

February 24, 2005 - 9-year-old Jessica Lunsford is discovered to be missing from her bedroom in Homosassa, Florida.

March 19, 2005 - Lunsford's body is found near her home after neighbor John Evander Couey confesses to killing her.

May 2, 2005 - Florida Gov. Jeb Bush signs the Jessica Lunsford Act which establishes a mandatory sentence of 25 years to life for people convicted of certain sex crimes against children 11 and younger, with lifetime tracking by GPS after their release.

February 12, 2007 - Couey's trial begins in Miami.

March 7, 2007 - Couey is found guilty of kidnapping, raping and murdering Lunsford.

July 17, 2007 - Mark Lunsford, Jessica's father, makes a courtroom statement to Couey: "I hope you hear her cry as you try to sleep at night."

August 24, 2007 - Couey is sentenced to death for the abduction, rape and murder of Lunsford. Couey dies in prison, of natural causes, in 2009.

Cherrie Mahan

February 22, 1985 - 8-year-old Cherrie Mahan is kidnapped on her way home from school in Winfield Township, Pennsylvania.

Is the first child featured on a "Have You Seen Me?" postcard put out by a company called ADVO Inc., in connection with the FBI, the US Postal Service and the National Center for Missing and Exploited Children.

Etan Patz

May 25, 1979 - 6-year-old Etan Patz disappears in the SoHo section of New York City while walking to the school bus stop alone for the first time.

He is the first missing child to be pictured on a milk carton.

The prime suspect is Jose Antonio Ramos, who said he had taken Etan to his apartment, but did not kill him.

November 15, 2000 - Patz is declared legally dead.

February 7, 2005 - Stanley and Julia Patz are awarded a $2 million judgment in a wrongful death lawsuit against Ramos, who is now in prison for molesting two boys.

May 2010 - The Manhattan District Attorney's office confirms that Patz's case has been reopened.

April 22, 2012 - A stain believed to be blood is found in the SoHo basement of an apartment that formerly belonged to Othniel Miller, a carpenter that knew Patz. The apartment is less than 100 yards from Patz's home.

April 23, 2012 - Tests reveal the stain is not blood, and no "obvious" human remains are located.

May 24, 2012 - Pedro Hernandez, a former Manhattan stock clerk who lived in Patz's neighborhood, is arrested in connection with the death. Authorities are alerted to the suspect by a tip.

May 25, 2012 - Hernandez is charged with the murder of Patz. Hernandez is denied bail and ordered to undergo a full psychiatric evaluation.

November 14, 2012 - Hernandez is indicted on charges of second-degree murder and first-degree kidnapping.

December 12, 2012 - Hernandez pleads not guilty to murder and kidnapping.

February 2014 - Hernandez's trial is postponed for psychiatric examinations and additional preparations.

May 8, 2015 - after the jury sends State Supreme Court Justice Maxwell Wiley a note -- the third since April 29 -- saying it was unable to reach a unanimous decision on Hernandez's guilt or innocence. One juror holds out against conviction. A mistrial is declared after the jury sends State Supreme Court Justice Maxwell Wiley a note -- the third since April 29 -- saying it was unable to reach a unanimous decision on Hernandez's guilt or innocence. One juror holds out against conviction.

February 14, 2017 - A jury finds Hernandez guilty of the kidnapping and murder of Patz.

April 18, 2017 - Hernandez is sentenced to 25 years to life in prison.

Ayla Reynolds

December 17, 2011 - Justin DiPietro reports his 20-month-old daughter Ayla Reynolds is missing from their home in Waterville, Maine.

February 3, 2012 - Divers search two bodies of water near the home of Reynolds for a second time, but find no sign of her.

May 2012 - Authorities say they suspect the toddler is dead.

September 2017 - Reynolds is declared legally dead.

Samantha Runnion

July 15, 2002 - 5-year-old Samantha Runnion is abducted outside a Stanton, California, apartment complex while playing with a friend.

July 16, 2002 - Runnion's body is found near Lake Elsinore in Riverside County, California.

April 28, 2005 - Alejandro Avila is convicted of kidnapping, sexually assaulting and murdering Runnion.

July 22, 2005 - Avila is sentenced to death.

March 13, 2019 - Gov. Newsom signs an executive order issuing a moratorium on executions of death row inmates in California prisons, including Avila. This only suspends executions while Newsom is in office.

Elizabeth Smart

June 5, 2002 - is abducted from the bedroom of her home in the Arlington Hills neighborhood of Salt Lake City. 14-year-old Elizabeth Smart is abducted from the bedroom of her home in the Arlington Hills neighborhood of Salt Lake City.

March 12, 2003 - She is found alive walking down a street in Sandy, Utah, with two adults, Brian David Mitchell and Wanda Eileen Barzee.

Both Mitchell and Barzee are charged with six felony counts, including aggravated burglary, aggravated kidnapping and aggravated sexual assault.

January 9, 2004 - Barzee is ruled to be mentally incompetent to stand trial is sent to a state mental hospital.

July 26, 2005 - Mitchell is declared mentally incompetent to stand trial and sent to a mental hospital until he is judged to be fit.

December 18, 2006 - Mitchell is again found mentally unfit to stand trial after screaming outbursts in the courtroom.

October 24, 2008 - A federal judge, US Magistrate Judge Samuel Alba, enters a not guilty plea on behalf of Mitchell.

May 21, 2010 - Barzee, who pleaded guilty to kidnapping Smart, is sentenced to 15 years in prison.

May 25, 2011 - US District Judge Dale Kimball sentences Mitchell to life in prison.

September 11, 2018 - The Utah Board of Pardons and Parole announces that The Utah Board of Pardons and Parole announces that Barzee will be released on September 19, 2018, because her time in federal custody must be counted toward her state sentence. Barzee wasn't expected to be released for another five years.

September 19, 2018 - Barzee is released from prison. Under the conditions of her release, Barzee is released from prison. Under the conditions of her release, she must register as a sex offender and participate in a mental health treatment program.

Danielle van Dam

February 2, 2002 - 7-year-old Danielle van Dam is discovered missing from her home in suburban San Diego.

February 22, 2002 - David Westerfield, a neighbor, is arrested on suspicion of kidnapping after DNA test results showed van Dam's blood in his motor home and on his clothes.

February 27, 2002 - Van Dam's body is found in the southern California desert.

January 3, 2003 - Westerfield is sentenced to death for Danielle van Dam's abduction and murder.

March 13, 2019 - Gov. Newsom signs an executive order issuing a moratorium on executions of death row inmates in California prisons, including Westerfield. This only suspends executions while Newsom is in office.

Adam Walsh

July 27, 1981 - 6-year-old Adam Walsh is abducted from a mall near his home in Hollywood, Florida. His mother had let him look in the toy department at Sears while she looked for a lamp. When she returned, Adam was missing.

Two weeks after Adam disappeared, his severed head is discovered in a canal 120 miles away from the mall. The rest of his body is never recovered.

His father, John Walsh, becomes an advocate for missing children, lobbying for legislation and nationwide alert systems, and hosting the television program, "America's Most Wanted."

1996 - The prime suspect in the killing, Ottis Toole, dies in prison while serving a life sentence for another crime; he is never charged with Adam's murder.

December 16, 2008 - Hollywood police announce they are closing the Adam Walsh investigation and name Toole as Adam's suspected killer.

Rilya Wilson

April 2002 - Florida's Department of Children and Families (DCF) discovers 4-year-old Rilya Wilson is missing from the home of her caregiver, Geralyn Graham. DCF did not learn of her disappearance until well after she disappeared. Case reports were falsified to show Wilson's foster home had been visited.

March 2005 - Graham is indicted for Wilson's murder. The indictment claims Wilson was killed sometime in December 2000; the time she went missing. Wilson's body has never been found.

November 26, 2012 - Graham's trial begins for the murder, kidnapping and child abuse of Wilson.

February 2013 - Graham is sentenced to 55 years in prison after being convicted of kidnapping and child abuse in January. She was not convicted of first-degree murder.