A Bucks County woman who police say shot her two sons in the head as they slept, was charged with first-degree murder on Monday.

Trinh Nguyen, 38, had planned the deaths of her sons Jeffrey and Nelson Tini, 13 and 9, at least a week in advance, authorities said, writing an updated will that included instructions on what to do with their ashes.

After the shooting, Nguyen drove to New Jersey to buy heroin, then headed to the parking lot of a church near her Upper Makefield home, prosecutors said Monday. There, they said, she took the drug, and hastily scrawled a note, saying “Please call 911! My children are Dead in their bed” and giving her address, according to the affidavit of probable cause for her arrest.

The boys died at Children’s Hospital of Philadelphia on Friday, four days after the May 2 shooting in their bedrooms at the family’s Bucks County home.

Nguyen was initially charged with attempted murder. Her sons were kept on life support until they could donate their organs through the Gift of Life program.

At an arraignment in district court Monday, Nguyen said little as the charges against her were upgraded to murder. She had not yet hired an attorney, according to court records.

In a statement, Bucks County District Attorney Matt Weintraub said Nguyen’s actions were “unconscionable and horrific.”

“I have been praying for these boys and their surviving family for days. I am so sad to hear of their passing,” he said. “We will do what needs to be done to seek justice for all of them.”

Law enforcement officials have not released a motive for the shooting, but court records show that the family faced mounting financial problems in the months leading up to the shooting.

» READ MORE: A mother shot her two sons as they slept, police say. Now, a Bucks County community gathers to mourn.

Nguyen and her sons were set to be evicted May 3 from their half of the duplex they shared with the family of her ex-husband, according to court records. Nguyen owed more than $11,000 in unpaid rent to her former sister-in-law, Corrina Tini-Melchiondo, who owned the building, records show.

Documents from the eviction dispute show that Nguyen and Tini-Melchiondo had a rocky relationship, and her former sister-in-law and landlord had accused her of abusive and harassing behavior.

Nguyen divorced Nelson’s father, Ed Tini, last year, according to court records. Tini had unsuccessfully fought for sole custody of the boys, saying in a court filing last year that he worried that Nguyen would be a “classic parent kidnapper” and “flight risk,” and wouldn’t return from a vacation to Vietnam with the boys last summer. Through her attorney, Nguyen said she was a responsible parent with firm roots in the community.

On the day of the shooting, Tini-Melchiondo’s son, Gianni, 22, heard gunfire, went to investigate, and found Nguyen on the front lawn, holding a box of photos, according to Weintraub.

Nguyen asked Melchiondo if he would take the photos to her ex-husband, who works with him, investigators said. Melchiondo agreed, and when he took the photos from Nguyen, authorities said, she pulled out a Ruger .38 caliber revolver, aimed it at him, and pulled the trigger twice.

The gun did not fire, and Melchiondo was able to wrestle the gun away from Nguyen, who then fled in her minivan, according to the affidavit of probable cause for her arrest.

» READ MORE: A Bucks County woman shot her two sons and tried to kill a neighbor who came to investigate, police said

Inside the home, officers found the boys in their bedrooms, both shot in the head as they lay in their beds, Weintraub said. They were taken to St. Mary Medical Center in critical condition.

Hours after the shooting, administrators at the Washington Crossing Methodist Church called Upper Makefield Police to report that Nguyen’s van was parked on church’s property. They recognized the vehicle from social media posts about the crime by police.

Police apprehended Nguyen, who was rushed to the hospital because she had ingested heroin in an attempt to kill herself, according to prosecutors. Nguyen had additional ammunition for the gun, which she had legally purchased, with her in the van, authorities said.

Jeffrey and Nelson were remembered as fun-loving kids active in sports at Council Rock schools. Last week, friends, neighbors, and classmates gathered at a vigil for the brothers. Many who knew the family described Nguyen as a dedicated mother and said they were stunned by the charges against her. .