LOS ANGELES, CA – A 21-year-old woman was killed Thursday night after the vehicle she was riding in crashed during an alleged street race in Mission Viejo, and authorities arrested both drivers involved on suspicion of vehicular manslaughter with gross negligence.
The Orange County Sheriff’s Department said deputies were called at approximately 9:41 p.m. on Aug. 20 to the area of Los Alisos Boulevard and Mustang Run for what was initially reported as a solo-vehicle collision.
When deputies arrived, they found Shalia Deciderio, 21, of Rancho Santa Margarita, dead at the scene.
A preliminary investigation determined that the crash occurred while two vehicles were allegedly street racing, according to the Sheriff’s Department.
Authorities identified the driver of the vehicle that crashed as Jaime Rojas, 20, of Mission Viejo.
Rojas was taken to a hospital after the collision. Information released with the case indicated that he was in critical but stable condition.
The driver of the second vehicle was identified as Aiden Deciderio, 20, of Rancho Santa Margarita.
He remained at the scene after the crash.
Information provided about the case indicates that Aiden Deciderio is Shalia Deciderio’s younger brother.
That family relationship adds another devastating dimension to a case already involving a fatal street-racing allegation: one sibling was killed, while the other now faces potential criminal liability in connection with the circumstances that led to her death.
The Sheriff’s Department said both drivers were arrested for vehicular manslaughter with gross negligence.
Aiden Deciderio was booked following the crash.
Rojas was hospitalized and was expected to be booked after his release from medical care, according to information released about the investigation.
The Sheriff’s Department’s official statement does not identify the makes or models of the two vehicles, but information gathered about the crash described both as Infiniti vehicles.
Investigators said one of the cars left the roadway and struck a tree.
Authorities have not released a detailed reconstruction showing how fast either vehicle was traveling, how long the alleged race had been underway or whether one driver attempted to pass the other before the collision.
They also have not said whether alcohol, drugs, distraction or any mechanical issue played a role.
No such factor should be assumed while the investigation remains incomplete.
The crash is being investigated by the Orange County Sheriff’s Department’s Major Accident Investigation Team, commonly known as MAIT.
The official Sheriff’s Department release asks anyone with information that could assist investigators to contact MAIT at 949-425-1860.
MAIT investigators handle serious and fatal collisions and are responsible for reconstructing events through roadway evidence, vehicle damage, witness statements and other available material.
In a case involving suspected street racing, investigators can also examine whether the vehicles were accelerating against one another, whether excessive speed contributed to loss of control and how the conduct of each driver affected the fatal outcome.
The location itself is part of a major local roadway network.
City of Mission Viejo traffic documents identify Los Alisos Boulevard between Santa Margarita Parkway and Mustang Run as one of the city’s arterial roadway segments, while Mustang Run connects Los Alisos Boulevard with surrounding residential streets and Marguerite Parkway.
City records also establish a 35 mph prima facie speed limit on Mustang Run between Los Alisos Boulevard and Marguerite Parkway.
Authorities have not said whether either vehicle was traveling on Mustang Run at the time of the alleged race or how the measured speeds compared with posted limits.
Those details are expected to be part of the collision investigation rather than inferred from the roadway itself.
The criminal allegation also carries substantial legal consequences.
Under California Penal Code Section 192(c)(1), vehicular manslaughter with gross negligence involves an unlawful killing caused while driving in connection with an unlawful act not amounting to a felony, or a lawful act carried out in an unlawful manner, when the conduct involves gross negligence.
A conviction under that provision can be punished by two, four or six years in state prison, although the eventual charge and sentence in any specific case depend on the evidence, prosecutorial decisions and court proceedings.
California law also makes clear that gross negligence does not prevent prosecutors from considering more serious homicide charges when evidence supports implied malice or conscious disregard for life.
There is no indication that prosecutors have announced any additional homicide charge in this Mission Viejo case.
Both men are presumed innocent unless and until proven guilty in court.
The Orange County District Attorney’s Office will ultimately determine which charges, if any, are formally filed after reviewing the Sheriff’s Department investigation.
The crash also underscores the broader danger associated with illegal street racing.
The California Highway Patrol has expanded statewide operations targeting street racing, sideshows and excessive-speed driving, describing those activities as a continuing source of fatal and injury crashes.
CHP’s Sideshow, Takeover, Racing, Education and Enforcement Taskforce — known as STREET — combines enforcement operations with training and public-awareness campaigns aimed at dangerous racing activity.
According to the California Office of Traffic Safety, the program conducted 62 specialized operations during its 2025 grant cycle focused on street racing, sideshows and other major crash factors. Those operations resulted in 2,164 enforcement stops, 1,237 citations and 278 arrests.
Those statewide figures do not establish anything about the conduct of the two Mission Viejo drivers, but they illustrate the level of attention California traffic-safety agencies have placed on illegal racing.
CHP has warned that consequences of street racing can include serious injury or death, arrests, license suspension, fines and vehicle impoundment.
In this case, those dangers became immediate and irreversible.
Shalia Deciderio died at the scene at age 21.
Loved ones said she was also the mother of a young child.
Authorities have not released additional information about her family or funeral arrangements.
The Sheriff’s Department has also not said whether Shalia was seated in the front or rear of Rojas’ vehicle or whether she was wearing a seat belt.
No information has been released regarding additional passengers.
Investigators have not said whether surveillance cameras, dashboard cameras or nearby residential security systems recorded the alleged race or the collision.
They also have not publicly disclosed whether physical evidence at the scene — including tire marks, roadway debris or vehicle data — has allowed investigators to estimate the cars’ speeds.
Those questions are likely to be significant as MAIT reconstructs the crash.
Authorities have also not said whether the two drivers had arranged the alleged race in advance or whether it developed spontaneously while they were driving near Los Alisos Boulevard.
The distinction could become relevant as investigators examine intent and the conduct leading up to the impact.
The official Sheriff’s Department statement is clear on one central point: its preliminary investigation concluded that street racing caused the fatal collision, and both drivers were arrested for vehicular manslaughter with gross negligence.
The fact that one of those drivers is the victim’s brother does not change the legal analysis investigators must perform.
Authorities will still examine the actions of each driver independently and determine whether those actions contributed to Shalia Deciderio’s death.
Aiden Deciderio remained at the scene following the crash.
Rojas continued receiving medical treatment after suffering serious injuries.
The Sheriff’s Department has not released updated information about his condition.
Anyone who witnessed the vehicles before the crash, saw the collision or has video that could assist investigators is asked to contact OCSD Major Accident Investigation Team at 949-425-1860.
Anonymous tips can also be submitted through Orange County Crime Stoppers.
The investigation remains ongoing.
