LOS ANGELES, CA – A 21-year-old Rancho Santa Margarita woman was killed in a suspected street racing crash in Mission Viejo, and her younger brother is one of two drivers arrested on suspicion of vehicular manslaughter with gross negligence, authorities said.
The fatal collision happened at approximately 9:41 p.m. on Aug. 20 near Los Alisos Boulevard and Mustang Run, according to the Orange County Sheriff’s Department.
Deputies initially responded to what was reported as a single-vehicle traffic collision.
When they arrived, they found Shalia Deciderio, 21, of Rancho Santa Margarita, dead at the scene.
A preliminary investigation later determined that the crash occurred as the result of street racing, the Sheriff’s Department said.
Authorities identified the driver of the vehicle that crashed as Jaime Rojas, 20, of Mission Viejo.
Rojas was transported to a hospital following the collision.
The driver of the second vehicle was identified as Aiden Deciderio, 20, of Rancho Santa Margarita.
Aiden remained at the scene following the crash, according to OCSD.
Information provided by the family identifies Aiden as Shalia Deciderio’s younger brother.
That relationship adds another layer of tragedy to the case: Shalia died in the crash, while her brother now faces a felony allegation over conduct authorities say contributed to the collision.
Both Aiden Deciderio and Rojas were arrested on suspicion of vehicular manslaughter with gross negligence, the Sheriff’s Department said.
The arrests are allegations, and both men are presumed innocent unless and until proven guilty in court.
Authorities have not publicly released a detailed reconstruction of the collision.
Investigators have not said precisely how the alleged street race began, how long it continued or what speeds the vehicles reached before one of them left the roadway.
They also have not publicly identified alcohol or drugs as contributing factors.
The Orange County Sheriff’s Department’s official release does not mention suspected impairment.
That distinction is important because the criminal investigation currently centers on alleged street racing and grossly negligent driving rather than a publicly announced DUI allegation.
The case is being investigated by the department’s Major Accident Investigation Team, or MAIT.
MAIT is responsible for the detailed reconstruction of serious and fatal collisions handled by the Sheriff’s Department.
Investigators typically examine roadway evidence, vehicle damage, witness accounts, available video and other physical evidence to determine how a fatal crash unfolded.
The department has asked anyone with information that could assist the investigation to contact MAIT at 949-425-1860.
The crash occurred along a significant east-west roadway in Mission Viejo.
A City of Mission Viejo traffic engineering survey for Los Alisos Boulevard between Santa Margarita Parkway and Entidad lists a posted speed limit of 45 mph for that roadway segment.
The same city study documented traffic signals at Santa Margarita Parkway, Mustang Run and Entidad and described the corridor as a four-lane arterial with a center turn lane, bike lanes, sidewalks and commercial, school, park and open-space uses nearby.
Those roadway characteristics do not establish what speed either driver was traveling Thursday night.
Authorities have not released speed estimates for either vehicle, and the official investigation remains ongoing.
City records also show that Mustang Run is a substantial connector roadway rather than a small residential cul-de-sac.
Mission Viejo’s pavement inventory lists a four-lane portion of Mustang Run between Los Alisos Boulevard and Marguerite Parkway measuring about 1,494 feet in length and 61 feet wide.
Traffic studies for the surrounding area have previously treated Los Alisos Boulevard and Mustang Run as a major signalized intersection in the local street network.
Again, those records provide geographic context only.
They do not establish fault, vehicle speed or the specific path taken by either driver before the fatal crash.
Shalia Deciderio’s family described her as a mother and as someone whose personality deeply affected the people around her.
In a fundraising appeal, relatives described her as “loving, caring, vibrant, and outgoing” and said she leaves behind a young child.
The family said her death has created both emotional and financial hardship.
That fundraising effort is private and separate from the criminal investigation.
Authorities have not publicly released additional information about Shalia’s child or other immediate family members.
The investigation is focused on determining how the alleged race led to the fatal collision and how the conduct of each driver contributed to Shalia’s death.
That distinction matters because two separate vehicles were allegedly involved, even though only one vehicle was initially reported as having crashed.
OCSD’s preliminary finding is that street racing caused the collision.
Authorities have not yet disclosed whether investigators recovered electronic vehicle data that could establish speed, acceleration, braking or steering inputs.
Modern vehicles can sometimes retain crash-related information in event data recorders or other onboard systems.
Whether such evidence exists or has been recovered in this case has not been announced.
Police also have not said whether surveillance cameras, home security systems or dashboard cameras captured the two vehicles before impact.
Video evidence could help investigators determine whether the drivers accelerated against one another, traveled side-by-side or engaged in other behavior consistent with racing.
No such footage has been publicly released.
The legal allegation against both men is serious.
Under California law, vehicular manslaughter with gross negligence generally requires prosecutors to prove that a death resulted from driving conduct that went beyond ordinary carelessness and rose to the level of gross negligence.
Exactly what prosecutors ultimately charge will depend on the evidence presented by investigators.
The Orange County District Attorney’s Office had not publicly announced formal charging details in the official sources reviewed for this article.
The Sheriff’s Department release confirms the arrests but does not provide bail information or court dates.
That means reports about future hearings, charging enhancements or other court consequences should remain preliminary until prosecutors or the court formally confirm them.
It is also unclear whether Rojas remained hospitalized or had been medically cleared for booking after the crash.
The Sheriff’s Department said only that he was transported to the hospital and that both drivers were arrested.
No updated medical condition was included in the official release.
Authorities likewise have not disclosed whether anyone else was inside either vehicle.
The official statement identifies Shalia as the person killed, Rojas as the driver of the crashed vehicle and Aiden as the driver of the second vehicle, but it does not list any additional passengers.
The location has been the subject of prior city traffic review.
A Mission Viejo traffic engineering study documented approximately 15,500 vehicles per day on the Los Alisos Boulevard segment containing Mustang Run and recorded an 85th-percentile speed of 48 mph during a 2022 survey.
That historic traffic data does not describe conditions on the night of Shalia’s death, but it shows that the crash occurred on a busy arterial used by thousands of motorists each day.
Street racing can dramatically change the risks present on such roads because ordinary traffic engineering assumes drivers are generally operating within expected speeds and movements.
When vehicles accelerate far beyond normal traffic flow, stopping distance increases, drivers have less time to react and roadside objects can become especially dangerous if a vehicle leaves the roadway.
Investigators have not said which of those factors specifically occurred here beyond the preliminary conclusion that racing caused the crash.
The Sheriff’s Department continues to seek witnesses.
Anyone who saw the vehicles before the collision, witnessed the crash or has video that may assist investigators can contact the OCSD Major Accident Investigation Team at 949-425-1860.
Anonymous information can also be submitted through Orange County Crime Stoppers at 855-TIP-OCCS.
For Shalia Deciderio’s family, the criminal investigation is unfolding alongside the loss of a 21-year-old daughter, sister and mother.
For investigators, the next phase will be establishing in detail what both drivers were doing before the crash and whether the evidence supports the felony allegations for which they were arrested.
No additional cause beyond suspected street racing has been publicly established.
The investigation remains active.
