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(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.
According to the FBI's National Crime Information Center (NCIC) Missing Person File, as of December 31, 2021, there are 93,718 active missing person records, of which juveniles under the age of 18 account for 30,400 (32%) of the records.
"AMBER (America's Missing: Broadcast Emergency Response) Alerts are emergency messages broadcast when a law enforcement agency determines that a child has been abducted and is in imminent danger. The broadcasts include information about the child and the abductor, including physical descriptions as well as information about the abductor's vehicle."
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 then 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.
As of December 2021, the AMBER Alert program has been credited with the safe recovery of 1,111 children.
This list represents selected notable and/or recent cases.
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. On February 6, her body is found.
February 20, 2004 - Mechanic Joseph P. Smith is indicted on charges of first-degree murder, kidnapping and sexual battery. He is found guilty on November 17, 2005.
December 1, 2005 - A jury recommends the death penalty for Smith by a 10-2 vote. On March 15, 2006, Judge Andrew Owens 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 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 to impose a death sentence.
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. On July 10, remains found at a Montana campsite are identified as Dylan's.
October 16, 2006 - Duncan pleads guilty to murder and kidnapping charges in state court and is sentenced to life without parole for the kidnappings. He pleads guilty to federal charges in December 2007 and receives three death sentences.
March 28, 2021 - Duncan dies in prison.
May 8, 2005 - Laura Hobbs and Krystal Tobias are reported missing from their homes in Zion, Illinois. Laura's father, Jerry Hobbs, discovers their bodies in a neighborhood park the following day. On May 10, Hobbs is arrested and charged with their murders.
August 4, 2010 - The murder charges are dropped and Hobbs is released from prison after DNA links the killings to Jorge Torrez, a former marine serving prison time in Arlington, Virginia on multiple charges including rape and abduction.
April 24, 2014 - Torrez receives a death sentence from a jury in Alexandria, Virginia for killing Amanda Jean Snell, a 20-year-old Navy petty officer, in 2009.
September 2018 - Torrez is sentenced to 100 years in prison in an Illinois court for the murders of Laura and Krystal.
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.
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.
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. In December 2007, his sentence is commuted to life in prison after New Jersey abolishes the death penalty.
Kanka's death inspires Megan's Law, which requires convicted sex offenders to register with local police and the community be notified of their presence.
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. He is convicted and sentenced to death in June 1996.
March 13, 2019 - Gov. Gavin Newsom signs an executive order issuing a moratorium on executions of death row inmates in California prisons, including Davis. This only suspends executions while Newsom is in office.
Klaas' kidnapping prompts California to pass the "three-strikes" law, which gives a life term to those convicted of their third felony.
February 24, 2005 - 9-year-old Jessica Lunsford is discovered to be missing from her bedroom in Homosassa, Florida. On March 19, her body is found near her home after neighbor John Evander Couey confesses to killing her.
March 7, 2007 - Couey is found guilty of kidnapping, raping and murdering Lunsford. He is sentenced to death on August 24. In 2009, Couey dies in prison of natural causes.
Lunsford's case prompts Florida Gov. Jeb Bush to sign 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 22, 1985 - 8-year-old Cherrie Mahan is kidnapped on her way home from school in Winfield Township, Pennsylvania. She is never found and her case remains unsolved.
She 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.
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.
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 who knew Patz. The apartment is less than 100 yards from Patz's home. 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. On May 25, Hernandez is charged with the murder of Patz. He 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. He pleads not guilty on December 12.
May 8, 2015 - 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. On April 18, he is sentenced to 25 years to life in prison.
Patz is the first missing child to be pictured on a milk carton.
December 17, 2011 - Justin DiPietro reports his 20-month-old daughter Ayla Reynolds is missing from their home in Waterville, Maine.
January 28, 2012 - Police reveal that they found blood stains, identified as Reynolds' blood type, in the basement of the DiPietro home.
May 2012 - Authorities say they suspect the toddler is dead. She is declared legally dead in September 2017.
July 15, 2002 - 5-year-old Samantha Runnion is abducted outside a Stanton, California, apartment complex while playing with a friend. The following day, her body is found near Lake Elsinore in Riverside County, California.
April 28, 2005 - Alejandro Avila is convicted of kidnapping, sexually assaulting and murdering Runnion. He is sentenced to death on July 22.
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.
June 5, 2002 - 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 Brian David Mitchell and Wanda Eileen Barzee.
March 18, 2003 - 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 mentally incompetent to stand trial and sent to a state mental hospital. On May 21, 2010, Barzee, who pleaded guilty to kidnapping Smart, is sentenced to 15 years in prison.
July 26, 2005 - Mitchell is declared mentally incompetent to stand trial and sent to a mental hospital until he is judged to be fit. He is again found mentally unfit to stand trial after screaming outbursts in the courtroom on December 18, 2006.
October 24, 2008 - A federal judge, US Magistrate Judge Samuel Alba, enters a not guilty plea on behalf of Mitchell. On May 25, 2011, Mitchell is sentenced to life in prison.
September 11, 2018 - The Utah Board of Pardons and Parole announces that Barzee will be released on September 19, because her time in federal custody must be counted toward her state sentence. Barzee wasn't expected to be released for another five years. Under the conditions of her release, she must register as a sex offender and participate in a mental health treatment program.
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 Westerfield's 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 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.
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. Two weeks later, his severed head is discovered in a canal 120 miles away from the mall. The rest of his body is never recovered.
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.
Adam's 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."
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. It is determined that the last time DCF social workers visited the girl was 15 months earlier, in January 2001. Graham claims she gave the child to a social worker in 2001 and never saw her again.
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.
February 2013 - Graham is sentenced to 55 years in prison for kidnapping and child abuse. She is not convicted of murder.
Wilson's case prompts Florida to pass the Rilya Wilson Act, which requires children from birth to the age of school entry, that are under the state's care to attend a licensed childcare program five days a week, unless granted an exception from the court. Unexcused absences from a program must be reported by the program.