Sanchez was born in San Sebastian, Puerto Rico, on January 19, 1958, as the youngest of three children. His father, Altemio Sanchez, Sr., left the family when he was two years old when he turned out to be having an affair with a prostitute. His mother, Lucy Caraballo, who had tried to cut her pregnancy with Altemio short by taking high doses of pills, then moved with the rest of the family to New York. When Sanchez was a child, he lived in North Collins, near Buffalo, New York and was abused physically and sexually by his mother's new boyfriend, who also beat her in front of him. When he was a teenager, he attended high school, where he was very involved in sports but had no girlfriends; in fact, he later admitted that he was afraid of talking to girls. He was described as happy but shy. During this time, his mother told him he was a mistake. When he was in junior high, he started having blackouts. In 1975, aged 17, Sanchez is believed to have committed his first rape. After graduating high school, he enrolled in an industrial-arts program at Buffalo State College. In 1978, he met one Kathleen Whitley at the college and started dating her. She became the first and only woman with whom he had a relationship. The previous year, he had committed the first rape positively attributed to him. When she became pregnant, he dropped out and took a job at a factory called Trico. Two years later they married and had two sons, Christopher and Michael, together. In 1983, he got a job at the American Brass Company, where he worked until his capture.
Over the course of the 1980s, Sanchez raped over a dozen women. In September of 1990, he escalated to murder, fatally strangling jogger Linda Yalem at the Ellicott Creek Bike Path. He became a suspect in October when a coworker reported him to the police, saying he had been there twice in the previous 14 months. Police then set up surveillance of him. On January 31 the next year, he was voluntarily interviewed by the police and was released. While his fingerprints were taken, a sample of his DNA was not. In 1991, he was arrested for solicitation, trying to pick up an undercover police officer posing as a prostitute. His charges were reduced to loitering. In 1992, he killed again, raping and fatally strangling a prostitute named Majane Mazur. He killed her because they'd had prior contact and she could have recognized his face. In 1999, Sanchez was once again arrested for soliciting a prostitute, and once again his charge was reduced to loitering. In May of 2005, his mother passed away. The next year, his father also passed away. On September 29, 2006, 16 years to the day after his first murder, he killed again, the victim being 45-year-old Joan Diver. Unlike his other victims, she wasn't raped. On November 15, his DNA was found in a droplet of sweat in the victim's car, linking the murder to the other Bike Path Rapist attacks. Sanchez once again became a suspect. In 2007, he had dinner with his wife at a restaurant. Afterwards, the police collected a sample of his DNA from their table. When it was matched to that of the Bike Path Rapist, he was brought in for questioning. After nearly ten hours of interrogation, he was arrested. Four days later, he was also indicted for the murders of Linda Yalem and Majane Mazur. On May 16, he pleaded guilty to the three murders in court and received three life sentences. He is currently serving his time at the Clinton Correctional Facility.
Sanchez's victims were women whose ages ranged from the mid-teens to the mid-40s, whom he would attack near bike paths and drag somewhere more secluded. During his first assaults, he would threaten them with a knife or a gun and rub against them, though he later started raping them penetratingly. When one victim put up too much of a fight, he began strangling them non-fatally (though three of his victims died) with a double ligature, tightening it to control them and sometimes suffocating them to the point of unconsciousness. In order to get away, he would make the victims wait for several minutes after the rapes. He would also force them to blindfold themselves with their own clothing (but also sometimes taped their eyes and/or mouths shut with duct tape) so they wouldn't be able to identify him afterwards. In the case of Joan Diver's murder, he also applied blunt-force trauma. During at least three of his attacks, he would call himself 'David' or 'Dave'.
- September 29, 1990: Linda Susan Yalem, 22
- October 31, 1992: Majane Elizabeth Mazur, 34
- September 29, 2006: Joan Lee Diver, 45 (killed by strangulation and blunt-force trauma, but not raped)
Note: Sanchez was only positively connected to 14 rapes, though there are some open cases believed to be his work. The following list was based on a record of his crimes listed by Radford University and articles from Murderpedia.
- Unspecified date in 1975: Unnamed victim (possibly)
- Unspecified date in 1977: Unnamed victim (subdued by bludgeoning and threatened with a knife; raped, but not sexually penetrated)
- April 14, 1981: Unnamed 21-year-old woman
- November 19: Unnamed 21-year-old woman
- December 19: Unnamed victim
- December 22: Unnamed 28-year-old woman (raped at the same location as the above victim)
- Unspecified date: Unnamed 21-year-old woman
- April 3: Unnamed 22-year-old woman
- July 8: Unnamed 21-year-old woman
- Unspecified date in 1985: Unnamed victim
- June 12: Unnamed 44-year-old woman (first rape with a ligature; strangled to unconsciousness with a cord after he was finished)
- July 14: Unnamed 17-year-old girl (used a white clothesline)
- June 10, 1988: Unnamed 16-year-old girl (used a wire)
- Unspecified date: Unnamed 22-year-old woman (attempted)
- May 1: Unnamed 15-year-old girl (used a rope)
- August 24: Unnamed 14-year-old girl (used a rope like the previous victim; tied up, repeatedly strangled to unconsciousness, and left for dead)
- May 31: Unnamed 15-year-old girl (strangled to unconsciousness with a cord)
- October 19, 1994: Unnamed 14-year-old girl (used a rope)