As relatives mourned a woman and her two young daughters murdered and left in a West Miami-Dade walk-in closet, police questioned and released her estranged husband early Thursday.

Miami-Dade police won’t say whether Alberto Luis Sierra is a suspect or a “person of interest” in the deaths of his wife, Gladys Machado, and stepdaughters Julia and Daniela Padrino, ages 8 and 4.

He turned himself in Wednesday night to Miami-Dade’s Kendall station. Homicide detectives questioned him overnight and he was released. No charges were filed as the investigation continues.

Sierra certainly has a troubling past. He boasts a long history of arrests over drugs, weapons and domestic violence.

And as recently as October 2011, Sierra was investigated by the state’s child welfare agency after one of Machado’s daughters told a teacher that her stepfather had bitten her on the arm.

“I do believe their lives are in danger,” the girls’ biological father, Michael Padrino, wrote at the time in asking a Miami-Dade judge for sole custody of his children. “I’m begging on the mercy of the courts to help me and my children.”

But the judge declined to award him sole custody because the Department of Children and Families returned the children to Machado after briefly removing them from the woman’s home, court records show.

Authorities, awaiting final autopsy results, did not reveal how the girls and their mother died.

The couple had split, and the family was no longer living at the house. Machado, 29, and her daughters were last seen Saturday night when they left to go shopping. Her 6-year-old son remained at Machado’s grandmother’s Homestead home, where the family had been staying.

Teresa Lorenzana, a neighbor and long-time family friend, wondered why it took so long for the bodies to be discovered.

“What surprises me is the fact the boy had been with his grandmother all weekend,” Lorenzana said. “I don’t know how so many days could go by and nobody knew what happened.”

Then on Tuesday afternoon, a woman who rents an efficiency at the home found the bodies in a small walk-in master bedroom closet. She had not heard anything unusual in the days before the discovery, and the empty house was mostly tidy.

How exactly Machado and her daughters came to be at the house remains unclear. Investigators on Wednesday were still looking for Machado’s car and her belongings.

Machado, who friends said drove a gold Nissan Altima, worked as a registrar at the Beauty Schools of America at 1176 SW 67th Ave., where Wednesday teary students and staff gathered to remember her.

“We are deeply saddened,” said Jeff Gonzalez, the school’s executive director of operations.

Her children attended Lil’ Pirates Learning Center in West Miami-Dade.

“She was a very good mother,” said Olga Espinoza, whose children went to school with the girls.

Records show that Machado’s life was filled with domestic strife. She and Padrino, the father of all three kids, separated in February 2010, later divorcing in a long-running court battle marred by fights over child support payments.

Not long after Machado separated from Padrino, she began dating Sierra, 28, who described himself as a marble worker.

According to an arrest report, the two had been dating for two months and were living together in Homestead. During a “heated argument,” Sierra punched Machado’s arm as she tried to call police, then bit her arm, according to court documents.