On 20 April 1997, Eva Blanco Puig, a Spanish high school student was murdered in Algete, Madrid. The case remained unsolved for over a decade, gaining significant media attention in Spain and is popularly known as the Eva Blanco Case ("Caso Eva Blanco"), the Crime of Algete ("Crimen de Algete") or Operation Gang ("Operación Pandilla"), the code name given to the investigation by the Spanish Civil Guard. 
In 2013, new advancements in genealogical DNA research led to the determination that the suspect had North African origins. Hundreds of people with North African origins that had lived in the Algete community subsequently contributed their DNA profile to help the investigative effort; one of the donors showed a sibling-level match with the perpetrator, and further investigations eventually led to the arrest of Ahmed Chelh Gerj, a Moroccan-Spanish citizen who had lived in Algete with his brother in 1997. 
Chelh committed suicide in prison in 2016, and the case was closed.
Disappearance.
Eva Blanco (born 17 February 1981) played tennis with her friends during the afternoon of 19 April. At night, the group stayed in a local disco until 23:30, when they prepared to return home. Blanco, who had agreed to return at midnight, was among the first to separate from the rest. A female friend accompanied her to a vacant lot some 700 meters from Blanco's home in the Valderrey residential area, before they parted ways at 23:45. Blanco intended to walk across the vacant lot as a shortcut to her home, avoiding a longer detour through the town center, but she never reached her destination. The same shortcut was used by her and other Valderrey students regularly to get to high school. Because Blanco had always been on time before, her mother became worried and she called Blanco's friends, who told her that she had already left. She alerted her husband, a tow truck driver, who searched for her in the town with the help of his nephew, a local police officer, and the father of one of Blanco's friends. Finding no trace of her, the parents reported her disappearance at the local Civil Guard station at 1:00 AM, but the officers were apathetic about filing a disappearance after little over an hour. The guard at the door even said that children of her age were all on drugs and she was probably lying in some doorway.
By 2:30, Blanco's family, friends, Civil Guards and the local police began her search in Algete and the area leading to nearby Fuente el Saz de Jarama, although a missing report was not filed by the Civil Guard until 8:00. At 12:00, the family contacted the regional TV station Telemadrid and requested its help publicizing the case.
Blanco's father visited the local Civil Guard station fifteen times during the night and criticized the institution for not searching the rural roads or using vehicles in the search before sunrise, except for a short 20 minutes run around Valderrey. He claimed that they did not do it earlier because they did not have the gas. The Civil Guard denied the accusation and said that it was customary to wait some hours between a missing person report and its search.
Investigation.
Discovery of body.
Blanco's body was found the next day by two elderly Ajalvir residents at 9:00 AM, next to a road construction site between Cobeña and Belvis de Jarama, six kilometers away from Algete. The residents thought that she might have been run over by a car, but the Civil Guard noticed that the victim, lying face down on the ground, had actually been stabbed several times
in the back while she tried to run away from an attacker. The body was dressed with the same jeans, dark sweater and mountain boots that Blanco was wearing when she disappeared, with only one sleeve of her jacket taken off. Both killer and victim were also assumed to have reached the area in a vehicle, although abundant rain in the night of the murder had washed out any tire tracks and most other forensic evidence. Nevertheless, some footprints from the victim and a man wearing size 42 moccasins survived.
The Civil Guard notified Blanco's family of the discovery at 15:30. The news caused commotion in Algete, a town of just 12,300 people, with no recent instances of violent crime. At 19:00, 200 people gathered silently before Blanco's home to condemn her murder. Blanco's funeral on 23 April was attended by 2,000 people.
Autopsy report.
The autopsy report showed that Blanco was stabbed in the back 19 times before dying from blood loss around 4:00 AM. The murder weapon was a navaja between 8 and 10 centimetres long and 1  cm wide. The first stab to the side of the body was made while she was sitting in a vehicle and the rest after she exited it and tried to run up the slope next to the road. Many of these later wounds, mostly found on Blanco's ear and back of the head were superficial and interpreted as "passionate." In contrast, the first injury was deep and may have been fatal even in the absence of all others. Blanco's hymen was torn and the same man's semen was found in her mouth, vagina and underwear. A red fibre was also retrieved from Blanco's mouth, and subsequently identified by the Catalonia Textile Museum and Documentation Centre as belonging to a common type of car upholstery, confirming that Blanco had been in a vehicle after her disappearance.
First theories.
Because the body was found dressed and showed no previous signs of violence, both coroner and officers believed that the sex had been consensual and that the murder was the result of an argument after. In contrast, Blanco's parents thought that their daughter had been kidnapped and raped at knifepoint, then murdered to avoid prosecution for the previous crime.
The Civil Guard initially believed that the case would be closed after a short investigation. The dominant theory was that a single person known to Blanco had approached her in a car, offered her a ride which she accepted, and took her to the construction site, a known lovers lane, where they had sex before she was murdered. The first suspect was Blanco's ex-boyfriend, a resident of Fuente el Saz who had recently broken up with her. However, he was ruled out after being questioned by police. Afterward, the investigation centered on adult men known to Blanco's family and that she might trust. On 29 May, the government announced that the Civil Guard found the case more complicated than expected and that it no longer excluded a stranger as the perpetrator. Blanco's friends claimed that she would never accept a ride from a stranger and that she must have been forced into the car. Other neighbors linked the crime to a strange blue car seen in the town following another girl around midnight, one of whose occupiers was a blond man around twenty years old. However, nobody recorded the car's plates.
The existence of semen was kept from Blanco's family and the public while the officers retrieved DNA samples from Blanco's male relatives and acquaintances, all in secret, and compared it to the semen's DNA. Blanco's father's sample was extracted from a cigarette that he had smoked and left behind while drinking coffee and discussing the case with Civil Guard officers; others were taken under the guise of unrelated blood alcohol content tests or from cups and glasses used in bars. Although no matches were made, the Civil Guard remained convinced that the killer was an adult male resident in Algete or a nearby town.
'Secret diaries'.
Eight months after the crime, Blanco's mother found two notebooks hidden between drawers in her daughter's room. They were labeled "95-96" and "96-97", and were handwritten by the victim until the day of her murder. Many of these pages contained nothing but "Eva and Miguel", the name of her ex-boyfriend, repeated over and over in different pen colors. Two pages before the last one's end, however, "Eva and Miguel" were replaced by "Eva and 343110". All attempts to discover the meaning of "343110" were unsuccessful, with some hypothesis revolving around the fact that "34" is the phone prefix of Spain, and "110" is Algete's postal code. Blanco's father believed that it was the number of a pager given in a Coca-Cola promotion at the time, while others believed that it was a coded name.
Proposed mass DNA test.
After being informed that his DNA had been compared to semen found in his daughter's body and excluded him as a suspect, Blanco's father began to campaign for other Algete residents to provide voluntary DNA samples in an effort to help catch his daughter's killer. In this project he was backed by Algete's Mayor, Jesús Herrera Fernández (PSOE), who made an official announcement in November 1999, petitioning all male residents of Algete over 16 years of age (est. 5,000) to provide voluntary hair or saliva samples if they wished to. The proposition was unanimously rejected by Spanish judicial organizations who considered it "simple-minded," "disproportionate," "useless," and a potential stigma for Algete residents who refused to provide a DNA sample without court order and were in their legal right to do so. Nevertheless, Blanco's father received 2,013 samples from residents of Algete and nearby towns and deposited them in the local courthouse until it was decided what to do with them. The case's examining magistrate requested a report from Madrid's chief prosecutor on the legal feasibility of such test. The response, issued on 30 March 2000, was that testing should only be done on samples of people who could be deemed suspicious according to the investigation, and not just volunteers. Only samples from 45 people were tested, including 12 relatives of Blanco on her father's side, six on her mother's side, her acquaintances and any people with a previous criminal record, with special attention to cases of sexual misconduct and knife violence.
New evidence and renewed media interest.
By 2007, 30 officers had worked in the case and information on similar cases had been requested from other law enforcement offices including the Ertzaintza and the FBI. A specialist from the University of Santiago de Compostela re-examined the DNA evidence and concluded that it belonged to a man not of European descent. Six years later, in 2013, the number of people investigated had risen to 1,503, and 208 men from Algete and other towns had had their DNA tested, including criminals who were on leave at the time of the murder. A new examining magistrate allowed the opening and checking of the 2,013 envelopes containing the names of the volunteers from 1999, but not the testing of all DNA samples.
"Eva: Un expediente abierto".
On 26 April 2013 La Sexta's investigative show "Equipo de Investigación" aired a program about the case with the title "Eva: Un expediente abierto" ("Eva: A cold case"). The program recapitulated the known evidence and included interviews with Blanco's parents, friends, teachers, officers working on the case and , a psychologist and criminologist who gained notoriety when he helped identify serial killer Joaquín Ferrándiz Ventura in Castellón in 1998. Garrido disagreed with the Civil Guard's theory that the murderer was a "secret boyfriend" of Blanco, arguing that she would not agree to meet a lover 15 minutes before her curfew because of the risk of exposing such relationship. His criminal profile was a stalker who was not known or barely known to Blanco. The lack of defensive wounds could be explained because of the victim being threatened before agreeing to have sex with the attacker. The criminal would be of low intelligence, uneducated, with a low-skilled profession and emotionally immature, since he sought sex with a teenager rather than a woman closer in age. He probably had no family because they would have noticed him coming late and inquired him about it. It was also possible that he continued his criminal career elsewhere in Spain and that he was in prison for other attacks.
Facial composite.
After watching the program, a woman reported to authorities that she had seen a suspicious man in the road construction site around 8:00 AM. He was walking in the rain with no umbrella, looked like he had not slept during the night, and appeared to be looking for something before he got in a white Renault 18. The Civil Guard deemed the