There is a website, Killedbypolice.net, that goes through the effort of recording nearly every instance of police officers killing people on the streets and in the homes of the United States that has been reported through news media. It is a far more thorough reporting that what the U. S. Justice Department does.
According to the Justice Department, police kill some 400 Americans a year, but their data is tainted. They only collect data of "justifiable" killings, accidental or questionable killings are excluded. Also, most police agencies don't bother reporting at all. The actual number of Americans killed by police exceeds one thousand people per year. Police kill more Americans per year than Americans soldiers died during the worst year of Iraq War fighting (904 in 2007).
In 2014, American police killed at least 1100 people. On average, police kill someone in this country every seven hours. I took a look at two of the deadliest months.
In August, 2014 police kill 109 people. In March, 2015 police killed 115 citizens. Almost half were black or latino while over a third were white. For the remainder their race was other or listed as unknown.
The vast majority were shooting deaths. In one case a policeman killed a crew member for the TV show "Cops." Police fired 30 rounds towards a robbery suspect in Omaha, hitting both the suspect and the innocent. Nine people died from police using "non-lethal" tasers.
In most instances the only witnesses to these killings were either dead or cops. It is impossible to say how many of these shooting deaths were "righteous." As the now notorious case of the execution of Walter Scott shows, police shooters will spin outrageous yarns and, as the initial reporting of the killing shows, his fellow officers swallow those yarns without question. Prior to the video being made public there was no indication the shooting officer even faced a reprimand. An excuse you'll find with rote frequency is "officers feared for their lives." While that is certainly, at times, true, the excuse is used so freely it has ceased to be believable.
Traffic accidents are also a frequent cause of deaths, I found eight cases of death by police driving cars. On two occasions the officers were off duty and driving drunk. One case in Hawaii is of an on duty officer suspected of alleged hit-and-run homicide.
One of the saddest, in terms both of heartbreaking and pathetic, is the case of the youngest person to die. On August 15, fifteen year old Austin Dukette was struck and killed while on his bicycle by a patrol car driven by Lee County (FL) Sheriff Deputy Douglas Hood. Allegedly, Deputy Hood was distracted by his laptop computer when he hit Austin. Rather than charge him with vehicular manslaughter, Cape Coral police gave him a ticket for a moving violation, "failure to maintain a proper lane." Deputy Hood fought the ticket in court and Circuit Judge Frank Porter (a Jeb Bush appointee for whatever that is worth) found Hood not guilty of even a traffic violation.
In March, five people were killed while in jail. After Gregory Smith died on March 30, the Lake County (IN) Sheriff Department issued a press release saying, "officers used the restraint techniques they are trained to use."
In August, two officers straight up murdered three people in two separate acts. On August 11, New York patrol officer Robert Mroczek shot and killed his estranged wife Pammi and her boyfriend. He committed suicide four days later. Atlanta police officer Tahreem Zeus Rana allegedly killed his friend Verinica Woodard and then set fire to the body. Rana was arrested at the airport attempting to hop a flight to Mexico.
It is a sad but true fact that police officers are a leading cause of death in the United States.