An illegal immigrant butchered two women — a coworker and his roommate — in separate, savage attacks on Long Island, before calmly telling police, “I’ve killed someone,” cops said.

Rony Yahir Alvarenga Rivera, 22, allegedly stabbed a 42-year-old coworker to death as she took out the garbage at a Wendy’s in Island Park in Nassau County just after midnight on Friday, News 12 reported.

The victim was taking out the trash when Rivera allegedly ambushed her, cops said.

He allegedly killed his second victim, a 32-year-old woman, on Mineola Avenue in Valley Stream several hours later, according to Nassau County police.

Rivera, who came to the US illegally in 2016 at age 12, was living with his second victim, although police said the exact nature of their relationship isn’t clear.

Both women suffered savage stab wounds to the neck and torso.

Rivera then reportedly called the police and told them what he had done.

“While we were at the scene, we received information that an individual was stopped at 169 Atlantic Avenue in Lynbrook,” Det. Lt. George Darienzo said.

“He asked to see police and when police arrived, he said he killed somebody that night,” he added.

Rivera was arrested outside a 7-Eleven in Lynbrook.

He is facing multiple murder charges, but has pleaded not guilty.