"Burking" was (and on rare occasions still is) a method used by English criminals to kill somebody, with out leaving any injuries on the victim's body. In addition, even experienced coroners have difficulty establishing the true cause of death- it often looks like a heart attack.
Basically, the persons air supply is cut off (choke hold) and then somebody else sits on his chest, and thus compresses it. Evidently, a person is poor physical condition like Garner does not need to be "Burked" very long to kill him.
As a side note, this casino heir (and heroin addict- short "Burking" time, no defensive marks from a long struggle) was murdered by the technique Articles about Ted Binion - Los Angeles Times It took the coroner along time to figure out what happened.