Tenia Campbell, 24, of Medford, was arrested in the deaths of her daughters Jasmine and Jaida, who were found inside Campbell's vehicle at the entrance to a park in Montauk on Thursday.
Campbell's mother, Vanessa McQueen, said in a written statement to police that she received a call from her daughter around 2 p.m. Thursday.
"She kept saying she was sorry, but she didn't want to live anymore," McQueen wrote, saying her daughter was hysterically crying.
McQueen wrote that Campbell said that she would kill herself and her daughters, and while keeping Campbell on the phone, McQueen called 911 for help.
As the 911 operator listened, McQueen asked Campbell about the girls.
"They are already dead," McQueen wrote Campbell told her. "I killed them with my bare hands."
Shortly after, McQueen said Campbell hung up on her.
Authorities conducted a county-wide search between Medford to Montauk, where they found Campbell's vehicle at the Montauk County Park Third House Nature Center around 4 p.m. -- 60 miles away from their home.
WATCH: Police briefing on the arrest of Tenia Campbell
The children were found inside and were said to be in cardiac arrest, and officers attempted to resuscitate them with CPR. They were taken to Stony Brook Southampton Hospital, where they were pronounced dead.
Suffolk County District Attorney's Office Homicide Unit Borough Chief Kerriann Kelly said that Campbell had yelled at police officers to shoot her, but they were able to apprehend her.
She has been charged with two counts of second-degree murder.
There were no outward signs of trauma on the children, and the Medical Examiner will perform autopsies to determine the causes of death.
McQueen added in her written statement that her daughter had been diagnosed with bipolar disorder as a teenager and had been battling depression and anxiety her whole life.
She said that she had told her daughter to "take a break from the kids and let me have them so she could recharge herself, but she always says she can handle it."
Campbell also has a 4-year-old son who is apparently living with his father.
"Never would have thought she was going through the things she was going through," neighbor Roshonda Campbell said. "She seemed like she had it all together."
Campbell is due back in court July 3, but for paperwork only.
She faces 25 years to life in prison for each count of second-degree murder, which could be served consecutively because there are separate victims.
* More Long Island news
* Send us a news tip
* Download the abc7NY app for breaking news alerts
* Follow us on YouTube