The 26-year-old actress was questioned by police last week after Sam Magid filed a report claiming over USD 100,000 worth of watches and sunglasses were stolen from his Hollywood Hills home, reported TMZ.
Magid threw an all-night party that Lohan and her assistant Gavin Doyle attended when his possessions went missing.
Now Lohan and her assistant are formal suspects, but Lohan's lawyer has apparently refused a police request to interview the actress again.
"We are not commenting on this right now," her publicist Steve Honig said.
Earlier this year, the "Mean Girls" star was charged with stealing a necklace at a jewellery store in Venice, California.
Lohan was also involved in a car crash this year in which she wrecked a hired Porsche on the Pacific Coast Highway.
