Dr. Conrad Murray -- Manslaughter Target

Dr. Conrad Murray is now officially the target of a manslaughter investigation into the death of Michael Jackson.

A search warrant authorizing seizure of documents at a storage locker in Houston says law enforcement was hunting for "items constituting evidence of the offense of manslaughter that tend to show that Dr. Conrad Murray committed the said criminal offense."

The person who runs the facility says people from Murray's office visited the storage locker six times -- the last time the morning of Jackson's death.

We've been reporting for several weeks ... the LAPD has been treating Michael Jackson's death as a homicide and Dr. Murray was the focus of the investigation for possibly fueling the singer with a lethal dose of the powerful anesthesia Propofol.