The man, whose identity was not immediately released pending notification of family, had a history of mental illness and had attempted suicide earlier this month, Los Angeles police Detective Mark Morgan said.
A cleaner found the body in a stall in a men's bathroom on the upper level of Terminal 3 around 7:45 a.m. Wednesday. Investigators determined the man had most likely taken his own life.
There was no blood and no signs of trauma, Morgan said. The man apparently placed a plastic grocery bag over his head and tightened a jacket around his neck, then secured his hands behind his back using plastic zip ties, Morgan said.
Morgan said the man likely tied his hands "so he couldn't back out" of the attempt, Morgan said.
The man, who was born in 1975, had apparently been living out of a suitcase that contained many belongings, including a will. He left no known note, Morgan said.
Among his possessions were educational documents and materials that made investigators think he had been unsuccessfully trying to find work.
They also found paperwork showing he had tried previously to kill himself and had recently been placed under psychiatric observation.
The coroner's office planned an autopsy Thursday.