(CNN)Here is some background information about 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. Recent advances in technology, communications through public alerts and greater cooperation from law enforcement have helped solve many cases quickly.
The most recent study published by the Department of Justice, from 2002, reported that of the 797,500 children reported missing in a one-year period, 203,900 were abducted by family members and 58,200 were abducted by non-relatives. 115 were classified as being taken by a stranger.
"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 - which could lead to the child's recovery."
Between 1997 and January 2015, the AMBER Alert program has been credited with the safe recovery of 723 children.
All 50 states, the District of Columbia, Puerto Rico, and the U.S. Virgin Islands have AMBER Alert plans in place to help find missing children in danger.
The AMBER Alert system was named in honor of Amber Hagerman, who was abducted and murdered in 1996.
Notable and Recent Cases:
This list represents notable and/or recent cases.
December 17, 2011 - Father Justin DiPietro reports his 20-month-old Ayla Reynolds is missing from their home in Waterville, Maine.
February 3, 2012 - Divers search two bodies of water near the home of Ayla Reynolds for a second time, but find no sign of her.
October 4, 2011 - Ten-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 - Command post investigating Lisa's disappearance is shut down. FBI and Kansas City police had been involved; eight Kansas City detectives remain on the case.
Dylan and Shasta Groene
May 16, 2005 - Nine-year-old Dylan and eight-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 - Joseph Edward 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.
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 Jerry 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.
February 24, 2005 - Nine-year-old Jessica Lunsford is discovered to be missing from her bedroom in Homosassa, Florida.
March 19, 2005 - Her 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 Jessica Lunsford.
July 17, 2007 - Mark Lunsford, Jessica's father, makes a courtroom statement to John Evander Couey: "I hope you hear her cry as you try to sleep at night."
August 24, 2007 - John Evander Couey is sentenced to death for the abduction, rape and murder of Jessica Lunsford. Couey dies in prison, of natural causes, in 2009.
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 - Carlie'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 - Smith is sentenced to death by a jury.
March 15, 2006 - Judge Andrew Owens formally sentences Smith to death.
October 2002 - Eleven-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 - Michael J. Devlin receives 74 life sentences. He is serving his time at Crossroads Correctional Center in Cameron, Missouri.
July 15, 2002 - Five-year-old Samantha is abducted outside a Stanton, California apartment complex while playing with a friend.
July 16, 2002 - Runnion's body is found near Lake Elsinore, Calif., in Riverside County.
April 28, 2005 - Alejandro Avila is convicted of kidnapping, sexually assaulting and murdering Runnion.
July 22, 2005 - Avila is sentenced to death.
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, Utah.
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 - Wanda Barzee is ruled to be mentally incompetent to stand trial is sent to a state mental hospital.
July 26, 2005 - Brian David 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, U.S. Magistrate Judge Samuel Alba, enters a not guilty plea on behalf of Mitchell.
May 21, 2010 - Wanda Barzee, who pleaded guilty to kidnapping Elizabeth Smart, is sentenced to 15 years in prison.
May 25, 2011 - U.S. District Judge Dale Kimball sentences Brian David Mitchell to life in prison.
April 2002 - Florida's Department of Children and Families (DCF) discovers four-year-old Rilya 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 - Geralyn Graham is indicted for Rilya's murder. The indictment claims Wilson was killed sometime in December 2000, the time she went missing. Rilya's body has never been found.
November 26, 2012 - Geralyn Graham's trial begins for the murder, kidnapping and child abuse of Rilya Wilson.
February 2013 - Graham is sentenced to 55 years in prison after being convicted in January. She is not convicted of first-degree murder.
Danielle van Dam
February 2, 2002 - Seven-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 of Danielle after DNA test results showed Danielle's blood in his motor home and 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.
January 13, 1996 - Nine-year-old Amber 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.
July 29, 1994 - Seven-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.
December 2007 - Timmendequas' sentence is commuted to life in prison after New Jersey abolishes the death penalty.
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.
October 1, 1993 - Twelve-year-old Polly 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.
Davis had a long criminal record.
Klaas' kidnapping prompts California to pass the "three-strikes" law, which gives a life term to those convicted of their third felony.
February 22, 1985 - Eight-year-old Cherrie 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 U.S. Postal Service and the National Center for Missing and Exploited Children.
July 27, 1981 - Adam 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.
May 25, 1979 - Six-year-old Etan 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 - Etan 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 Etan 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 Etan. The apartment is less than 100 yards from Etan'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 Etan'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 Etan 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 - 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.