OAKLAND, Calif. (AP) — The caretaker of an indoor marijuana growing operation in Oakland's Chinatown district shot and killed a man early Monday after the man and two others tried to rob the operation, police said.

The shooting occurred shortly before 5 a.m. after three men tried to barge into a duplex about two blocks from the Oakland police headquarters downtown. The caretaker killed one of the suspects after they fatally shot his watchdog, police said.

"Officers responded to reports of gunfire," Oakland Police Lt. Kevin Wiley told reporters. "Upon arrival, they found one man deceased. . It appears to be a home invasion robbery."

Investigators have found the gun apparently used by the caretaker and another weapon that apparently belonged to one of the robbers.

The caretaker was taken into custody for questioning. It is not known if he will face any criminal charges, authorities said.

Investigators are also looking into whether the marijuana grow is a legal operation after the caretaker gave police some documents, said Officer Johnna Watson, a police spokeswoman.

"We have to verify if the documents are legal and valid," said Watson, who added that police also are trying to obtain search warrants to investigate other parts of the residence.

"There's a lot more work we need to follow up on," Wiley said.

The names of the caretaker and the dead suspect have not been released.

Police also were combing through Chinatown and searching surrounding areas for the other two suspects, both described as Asian males, as officers blocked the entrance to a nearby well-traveled tunnel leading to neighboring Alameda.

The tunnel was reopened in time for the morning commute.