Gao's disappearance a week ago baffled friends and police. He was described as a good student, an only child with no known involvement in crime or drugs. His mother, who owns a small business, was overseas at the time.
He had told friends he was excited by a meeting he was about to have, but did not give details. He was last seen getting into a white car with two apparently Asian men in the southwestern suburb of Padstow. Gao's own car, with his cellphone, keys and wallet inside, was later found nearby.
Robbery and Serious Crime Squad commander Detective Superintendent Luke Moore said an excited Gao had told friends the meeting was "really important". He told them he would see them later in the day.
Instead, Gao vanished. His disappearance was initially treated as kidnapping, but his family did not have the money to attract ransom demands.
"Our inquiries to date have led us to conclude that Mr Gao has been murdered," Moore told reporters. Police found 3kg of suspected methamphetamine in a white car seized at Cronulla. "We believe there was a drug transaction. Mr Gao had drugs with him when he went to the other car."
Police arrested McNamara, seizing a Ford Falcon and other objects from his Cronulla home. They also seized a car from Rogerson's home in Padstow Heights, and a boat from a storage unit.
McNamara had written of police corruption in Kings Cross in an autobiography: "This corrupt system was highly cultivated and provided for organised paybacks and set-ups for all of those outside the ambit of the protection of that corrupt system."
McNamara was an associate of Rogerson, a 73-year-old once-lauded former detective now also being sought. A known associate of other corrupt officers and organised crime figures, Rogerson was repeatedly accused of a wide range of crimes including an unproven allegation of contract killing. He was acquitted of conspiring to murder another detective, of attempted bribery and of involvement in drug dealing but was jailed for perverting the course of justice and lying to the NSW Police Integrity Commission.