An illegal migrant beat his 2-month-old daughter to death because he didn’t believe the baby was his, Long Island cops said Thursday.

A soulless Marlon Rabanales-Pretzantzin, 20, allegedly slapped little Liseyda Rabanales-Barrios in the face, punched her in the stomach and violently shook her inside his Inwood home on March 7, according to a sickening criminal complaint. 

He then allegedly threw her on a bed and callously pressed his fist into her chest.  

The accused sicko left her with ribcage injuries and a fractured vertebrae in the neck “as a result of being shook.”

The young dad was charged with murder Wednesday after he admitted to killing the helpless tot. 

Rabanales-Pretzantin — a Guatemalan migrant who crossed the border illegally in 2022 — told police that “although he is listed as the father on the birth certificate, he suspects that he is not the father so he lost affection for the baby and felt some kind of animosity,” Nassau County Detective Lieutenant Scott Skrynecki told The Post.

A 911 call was placed about the baby “rolling off the bed” inside the home near Maple Road and Elm Road around 10:40 a.m.,  cops said.

An autopsy done by a medical examiner revealed she died from a homicide, leading police to question Rabanales-Pretzantzin.

Police fumed that he should have never been allowed to step foot into the country.

“What he did to this kid is unthinkable,” raged Nassau County Police Detective Captain Stephen Fitzpatrick at a press conference Thursday, according to News 12 Long Island.

“We are all quite upset about this arrest and infuriated that this individual was even in this country to begin with.”

Cops said Rabanales-Pretzantzin made his way across the Mexico-El Paso border in 2022.

He was apprehended by Border Patrol and released, according to Skrynecki.

Rabanales-Pretzantzin then traveled to Virginia before landing in Nassau County.

He was arraigned in Nassau County Court on Thursday and held without bail.