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.

Illegal immigrant Rony Yahir Alvarenga Rivera, 22, is accused of murdering two women on LI. Nassau County Police Department

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 before killing his second hour hours later.…