Chester Bennington Investigation, No Drugs in Home at Time of Suicide

Chester Bennington's death investigation has turned up no obvious signs of drug use ... TMZ has learned.

Law enforcement sources tell us investigators found no illegal drugs or prescription drugs while searching the home following Chester's suicide. As we reported ... there was a partially drunk bottle of alcohol in the bedroom where he was found hanging.

The Linkin Park frontman was open about his drug abuse issues -- acid, meth, crack and more. His bandmates were well aware of his demons, and he credited his bandmates for staging an intervention.

It's unclear if Chester had any drugs in his system at the time of death. Toxicology results are pending.