11/20/2012 11:27 am ET Updated Nov 20, 2012

Alberto Sierra Arrested For Killing Wife Gladys Machado, Her Two Daughters (VIDEO)

The person of interest in the slayings of a Miami mother and her two children has now been charged with their murder.

Miami-Dade police say Tuesday morning Alberto Sierra, 28, confessed to strangling his estranged wife, Gladys del Carmen Sierra, also known as Gladys Machado, 29, and her two daughters Daniela and Julia Padrino.

Police say Sierra and del Carmen Sierra were involved in a verbal dispute at the Mall of the Americas near the Palmetto Expressway and West Flagler Street. Sierra held his wife and her two daughters hostage with a knife, driving them to her west Miami-Dade home.

At the residence, Sierra forced the trio inside, then suffocated his wife and her oldest daughter, Julia, 6, with plastic bags before sexually assaulting both of them.

He also suffocated his wife's younger daughter, Daniela, 4, as she slept. She did not show any signs of sexual assault, according to the police report.

A neighbor called police after finding the bodies of the three women in a closet inside their home last Tuesday. Del Carmen Sierra's 6-year-old son was safe with his grandmother at the time of the murders, police said.

Sierra now faces three first-degree murder charges, a rape charge, and another rape charge for the sexual assault of minor under 12 years old.