HEBER SPRINGS, Ark. -- Mindy McCready threatened suicide after losing custody of her sons earlier this month, yet she was allowed to leave a court-ordered drug rehabilitation program just days before she apparently killed herself at her Arkansas home, her ex-boyfriend said Monday.

Billy McKnight, who was in a long, stormy relationship with McCready and is the father of her oldest child, Zander, said the 37-year-old mother of two stayed in the substance abuse treatment centre for about 18 hours before she was allowed to walk free.

McCready died Sunday at her home in Heber Springs, a vacation community about 65 miles north of Little Rock. She was found dead on the front porch, where her longtime boyfriend, musician David Wilson, died last month of a gunshot wound to the head. Authorities are investigating both deaths as suicides but haven't determined an official cause of death.

McKnight told The Associated Press during a phone interview from Tampa, Fla., that McCready and Wilson, the father of her youngest son, were recently engaged. He wondered how she was allowed to go free, given all the turmoil in her life.

"That was a big mistake on the part of whoever released her," McKnight said. "She was in a terrible state of mind. She doesn't perform any more. She wasn't working. She has two kids and her fiance was just killed. There's no way she should be out by herself in a lonely house with nothing but booze and pills. That was a really, really bad mistake, and the end result is tragic."

Arkansas courts were closed for the holiday Monday, so local case documents weren't immediately available.

Neighbours reported hearing two shots Sunday afternoon when they called the Cleburne County Sheriff's Office. Authorities found Wilson's dog dead next to McCready's body at the home, where yellow crime-scene tape looped through a grove of pine trees and around the one-story brick house Monday afternoon.

"Based on what we have found at the scene at this time, we do believe that she took the life of the dog that we are being told by family members belonged to Mr. Wilson before she took her own life," Sheriff Marty Moss said.

The sheriff said McCready's two sons were safe. McKnight said the boys remained in foster care, where they were at the time of their mother's death. McKnight said he was trying to get custody of his son, Zander, but that he was not privy to what was happening with her other son, Zayne, who was born last year.

McCready's sons were put in foster care and she was ordered into rehab earlier this month after McCready's father expressed concern. He told a judge his daughter had stopped taking care of her children and herself after Wilson's death, and that she was abusing alcohol and prescription drugs.

Moss said McCready's cause of death would be released soon, but that "all indicators" point to suicide. Her body has been sent to the state crime lab for autopsy.

For all the highs McCready had early in her career, thanks to the spunky anti-chauvinist hit "Guys Do It All The time," and her first album, "Ten Thousand Angels," which has sold more than 2 million copies, there were many more lows. She previously attempted suicide at least three times, and her fragile state of mindwas always a concern to family and friends. She acknowledged in a 2010 interview that her life was turbulent at times, sometimes self-inflicted.

Over the years her relationships often made the biggest headlines. McKnight was charged with attempted murder after being arrested for beating and choking her. She claimed to be in a long relationship with baseball great Roger Clemens that started when she was 15 and he was 28 and married, but Clemens denied the relationship. She was once engaged to actor Dean Cain.

She also was arrested several times on drug charges, probation violations and a misdemeanour assault charge against her mother.

But there was a period in her life where McCready thought she might be able to escape that pattern. She reluctantly joined the "Celebrity Rehab 3" cast with Dr. Drew Pinsky, and left the show believing she might be able to change.

"She was doing great," Bob Forrest, a chemical dependency counsellor who frequently works with Pinsky and appeared on the show, told the AP on Monday. "She would go through these periods of three to six months where she didn't want to drink, didn't have an interest in drinking. And if she didn't drink, she didn't do drugs."

Just months after her appearance on the show in early 2010, McCready told the AP about the release of a new album, "I'm Still Here," her new love in Wilson and plans to reunite with her son, who was in her mother's custody at the time. But the progress seemed to unravel by late 2011. Her album debuted at No. 71 on the country albums chart and failed to gain significant radio airplay, and plans for a book and reality show failed to materialize.

She also was unable to immediately regain custody of Zander. McCready then took the boy from her mother, his legal guardian, and fled to Arkansas over what she said were child abuse fears. She was later found hiding in a home without permission.

McCready is the fifth participant in Pinsky's "Celebrity Rehab" shows to pass away since appearing on the show, and the third from Season 3. Pinsky has been criticized for the deaths and for showing such personal struggles on television.

In a statement, Pinsky said he had recently reached out to the singer after hearing about Wilson's death.

"She was devastated," Pinsky wrote. "Although she was fearful of stigma and ridicule she agreed with me that she needed to make her health and safety a priority. Unfortunately it seems that Mindy did not sustain her treatment."