Detectives say Trinh Nguyen planned the killing at least a week earlier and left behind a handwritten will.
UPPER MAKEFIELD TWP., Pennsylvania (WPVI) -- A mother accused of shooting her two sons inside their Bucks County, Pennsylvania home is now facing first-degree murder charges after the boys died of their injuries, officials say.
The Bucks County District Attorney's Office announced the upgraded charges for 38-year-old Trinh Nguyen on Monday.
Authorities say Nguyen shot her two boys, Jeffrey "JT" Tini, 13, and Nelson Tini, 9, on May 2 inside their Upper Makefield Township home.
In an updated criminal complaint, detectives from Bucks County and Upper Makefield Township say Nguyen planned the killing at least a week earlier and left behind a handwritten will dated April 25, 2022, that instructs the recipient on what to do with her and her sons' remains.
The two brothers died at Children's Hospital of Philadelphia from their injuries on Friday, the D.A. and Council Rock School District announced.
Jeffrey attended eighth grade at Newtown Middle School, and Nelson attended third grade at Sol Feinstone Elementary.
"We are deeply saddened to lose two of our Council Rock students and will miss them greatly," Susan Elliott, Acting Superintendent of Schools, said.
"This tragic event has shocked our Council Rock community. As a school community, we will continue to provide support for students, staff, and families as we cope with this horrific event. Our Crisis Response Team has continued to meet as this tragedy unfolds. The team has placed several counselors at the buildings the boys attended-Newtown Middle School and Sol Feinstone Elementary School. Those counselors are meeting with students, contacting parents, and supporting classroom teachers."
SEE ALSO: DA: Bucks County woman shot 2 sons; children not expected to survive
Nguyen is also charged with trying to shoot and kill her 22-year-old neighbor, who is also the nephew of her ex-husband, the same day she allegedly shot her children.
She reportedly handed him a box of photos to give to her ex-husband. Police say when he turned around to face Nguyen, he saw her pointing a black revolver at his face.
The neighbor wrestled the gun away from Nguyen after it didn't fire.
She then fled to Washington Crossing United Methodist Church where she was found inside her minivan.
Nguyen was taken to St. Mary's Medical Center due to the indication that she was under the influence and has been in custody since then.
"I have been praying for these boys and their surviving family for days," District Attorney Matt Weintraub said. "I am so sad to hear of their passing. This defendant's murder of two of her sons is unconscionable and horrific. We will do what needs to be done to seek justice for all of them."
According to officials, during her arraignment later that day, Nguyen said she did not flee.
According to a criminal complaint, she claimed to have traveled to New Jersey to obtain narcotics, which she ingested in an attempt to kill herself.
She added that she had not used drugs in the past, the complaint says.
Officials say a search warrant was executed on the minivan, and detectives located .38-caliber ammunition, several empty suspected heroin packages, several full suspected heroin packages, and swabs of suspected blood, among other evidence.
A note was located on the passenger-side dashboard and seized.
The note read: "Please call 911! My children are dead in their bed [and the address of the home]."
Detectives also served a search warrant at the Nguyen residence. According to officials, they located the handwritten will dated April 25, 2022 - a week before the shooting.
The will was signed, "Trinh Nguyen."
In addition, officials say a .38-caliber Ruger revolver was located from the front of the neighbor's home.
Court records show Nguyen was in an ongoing dispute with her landlord about more than $11,000 in unpaid rent.
On April 18, the judge issued an order informing Nguyen to move out of the home she shared with her children by May 3.
SEE ALSO: Friends hold vigil for 2 young brothers shot in Bucks County; mom charged
Elliott said several district and external supports will be in place at the schools on Monday.
"We plan to have therapy dogs available at both schools to provide additional support," Elliot said.