EAST HAVEN — A 911 caller told police that a woman had threatened to kill herself before her two children were found dead and she was found with arm injuries in a home filled with natural gas, according to a police department recording released Wednesday.

East Haven police released the 911 recording from Tuesday of the woman's friend, who sounded overwhelmed with emotion. The friend tells a dispatcher that she is outside the house, she can't get in and the children's mother told her over the phone that she had cut herself.

"My friend sent me a letter that she was going to kill herself and that her mom was the ... beneficiary," the friend also told the dispatcher.

A 5-year-old boy and his 7-year-old sister died, and their 36-year-old mother was being treated at a hospital for non-life threatening arm wounds, officials said. When police arrived, the mother was despondent, authorities said.

Authorities hadn't released the family members' names as of Wednesday afternoon. The children's father was notified and was "devastated," police said.

It's not clear how the children died. Autopsies were planned by the medical examiner's office. Police said the children likely had been dead inside the house for at least 24 hours.

Police said they believe the natural gas was deliberately turned on, but it was unclear if a leak or breakage could have been the cause.

Three police officers exposed to the gas were hospitalized as a precaution but weren't seriously affected, police said.

During the 911 call, the friend was asked about the children and said: "They're laying down in the house. The door is locked."

The friend then tells the dispatcher that she can't see the kids and knew they were in the house because their mother had told her so during a phone call.

"She's talking really light. I could barely understand her," the friend says. "Can you please ... I was talking to her on the phone and then when she told me she cut herself I hung up and called you guys."