Alberto Luis Sierra kills his estranged wife and two step daughters

Police say Alberto Sierra also admitted to raping his wife and his 8-year-old stepdaughter after suffocating them.

Faced with damning DNA evidence, police say, Alberto Luis Sierra finally confessed to suffocating his estranged wife and two young step-daughters with a plastic bag — and raping the oldest girl after she was dead.

His arrest early Tuesday capped a furious police investigation into the brutal triple slaying of Gladys Machado, 29 and Julia and Daniela Padrino, ages 8 and 4. A neighbor found their bodies last week laid out inside the master bedroom closet of a home where the couple used to live.

The shocking details emerged Tuesday as Miami-Dade police charged Sierra, 28, with three counts of first-degree murder and two of sexual battery.

He was being held without bail at the main Miami-Dade County Jail. Prosecutors likely will seek the death penalty, though the decision is weeks away.

Sierra, a convicted felon, was long the main focus of the investigation and confessed Monday night after hours of questioning.

The couple recently split up. Machado, a mother of three, had been living with her grandmother in Homestead while Sierra had moved into his mother’s townhome in Kendall.

Machado was last seen the evening of Nov. 10 when she left Homestead for a shopping trip with her two daughters. She left her 6-year-old son with her grandmother.

According to an arrest report, Sierra accompanied Machado and her daughters to the Mall of the Americas in Machado’s gold Nissan Altima.

When Machado received a phone call from another man, the two began to argue. Sierra grabbed a knife in the car and stabbed her.

He then drove Machado and her children back to their former home in Flagami, less than two miles from the mall.

There, Sierra locked the daughters in an adjacent bedroom and tied up Machado in the master bedroom, demanding the password to her phone.

Using a plastic bag, he suffocated her. After she died, Sierra raped her, according to the report.

Then, he turned his attention to the children, according to the police report by Miami-Dade Detective Juan Chaidez. The oldest daughter, Julia had knocked on the door asking to go to the bathroom. Sierra allowed her out and suffocated her. He suffocated Daniela, who had fallen asleep. According to the report, Sierra returned the master bedroom, where Julia’s body was, and raped her.

He placed all three bodies in the closet, cleaned the inside of the house and left.