November 7, 2006 -- In a stunning turnaround, a construction worker yesterday confessed to killing indie actress Adrienne Shelly, whose death in a Greenwich Village apartment last week was first thought to be suicide, cops said. "I was having a bad day," illegal immigrant Diego Pillco, 19, allegedly told cops. "I didn't mean to kill her. But I did kill her." Pillco told detectives that he punched Shelly, 40, last Wednesday afternoon outside the Abingdon Square apartment she was using as an office after she yelled at him about the noise he was making while working in a vacant apartment below. Pillco, who is from Ecuador and speaks only Spanish, also claimed that Shelly slapped him first. After seeing she was unconscious and believing she was dead, Pillco claimed, he dragged Shelly into her apartment, wrapped a bed sheet around her neck and attached it to a shower rod in the bathroom to make it appear she had hanged herself, sources said. The medical examiner has not yet released autopsy results. Shelly's marketing-exec husband, Andrew Ostroy, found her body just before 6 that evening. They have a 3-year-old daughter, Sophie. Earlier this year, Shelly, a Long Island native, appeared in the film "Factotum" with Matt Dillon, and at the time of her death was on the verge of releasing a movie called "Waitress," which she directed and wrote.