“There has been no evidence of an outsider having broken in, or any other crimes committed by another person,” an official from Seongnam Sujeong Police Agency told AFP.
“Suicide is among the possible causes.”
Authorities said the 25-year-old had been suffering from “severe depression”.
South Korea has one of the world’s highest rates of suicide which, according to recent government figures, is among the top causes of death for those under 40.
“I wish I could hope for Sulli to be the last idol to die from suicide and mental illness,” tweeted one fan.
“But knowing how cruel society is, I can’t help but be afraid about who’s going to be the next one.”
Beneath the glitz and glamour, the K-pop industry is known for its cut-throat competitiveness, a lack of privacy, online bullying and relentless public pressure to maintain a wholesome image at all times and at any cost.