On April 1, 1967, 22-year-old construction worker Denzil Dowell was shot by an officer of the Contra Costa County Sheriff's Department on suspicion of burglary. There is some dispute as to what exactly happened, as the police claimed that Denzil had run, jumping two fences before being shot in the back while fleeing; however, Denzil had a bad hip and a limp, and was shot with arms raised. Denzil bled to death, apparently without the police thinking to call an ambulance. Regardless, legally the police were, at the time, within their rights to shoot an unarmed man fleeing a crime scene (this law was changed in 1985), and the court ruled it a justifiable homicide.
A lot is uncertain about this case; Denzil's brothers reported that on previous run-ins police had threatened to kill him. His family reported that blood appeared in two places, including in front of the first fence that he was supposed to have jumped, and also 20 yards further on, leading to suspicions that the police had moved the body. Reports vary as to the number of shots heard, shots fired, and what exactly was in the coroner's report.
This was all complicated by the fact that the primary group reporting on all this were the Black Panthers -- in fact this was one of the first major community organizing campaigns run by the Panthers. This was great for the group's membership and raising awareness of police violence, but the fact the the Panther investigators openly carried guns -- and cocked them whenever a policeman showed up -- and consistently referred to the police as pigs (and sometimes "racist dog Gestapo pigs") did not help them convince the white majority; while they might have been right, they made it clear they were not impartial investigators.
Denzil's had not been the only questionable death of black citizens in recent months, but the protests over Denzil's death, the questions raised during the investigations, and the fact that answers as to what exactly happened were never nailed down, all contributed to the spread of the Black Power movement of the 70s.
Today, if you try to research Denzil's death there are two major sources found on the internet which directly contradict each other, and each of which include and neglect relevant facts. One is Wikipedia's brief entry (and the various sites mirroring Wikipedia). The other is the collection of reports of Black Panther members investigating at the time. I was unable to locate the original police report, coroner's report, or any court documents, nor, for that matter, the newspaper articles referenced by the Wikipedia article. Hopefully someone with access to some primary sources will someday post a more detailed account of the murder, but for most of the internet Denzil remains primarily as a formative event in the Black Panther movement, and the details are less important than the events that followed.