More than 2,000 criminal suspects died in police custody over a three-year period, half of them killed by officers.
The study by the Justice Department's Bureau of Justice Statistics is the first nationwide compilation of the reasons behind deaths associated with arrests in the aftermath of high-profile police assaults or killings involving Abner Louima, a Haitian, and Guinean Amadou Diallo in New York in the late 1990s.
The review found 55 percent of the 2,002 arrest-related deaths from 2003 through 2005 were due to homicide by state and local law enforcement officers. Alcohol and drug intoxication caused 13 percent of the deaths, followed by suicides at 12 percent, accidental injury at 7 percent and illness or natural causes, 6 percent. The causes of the deaths for the remaining 7 percent were unknown.
The highly populated states of California, Texas and Florida led in both police killings and overall arrest-related deaths. Georgia, Maryland and Montana were not included in the study because they did not submit data.
Most of those who died in custody were men (96 percent) between the ages of 18 and 44 (77 percent). Approximately 44 percent were white; 32 percent black; 20 percent Hispanic; and 4 percent were of other or multiple races.
"Keep in mind we have 2,000 deaths out of almost 40 million arrests over three years, so that tells you by their nature they are very unusual cases," said Christopher J. Mumola, who authored the study.
"Still, they do need to be looked at to determine whether police training can be better or practices can be better," he said.
State laws and police department policy typically let officers use deadly force to defend themselves or others from the threat of death or serious injury. Deadly force also is allowed to prevent the escape of a suspect in a violent felony who poses an immediate threat to others.
The Justice Department study released Thursday suggests that most of the police killings would be considered justified, although it does not make that final determination. About 80 percent of the cases involved criminal suspects who reportedly brandished a weapon "to threaten or assault" the arresting officers.
Another 17 percent involved suspects who allegedly grabbed, hit or fought with police. More than one-third of the police killings, or about 36 percent, involved a suspect who tried to flee or otherwise escape arrest.
The report was compiled at the request of Congress in 2000 after the 1997 struggle between New York police and Louima, a security guard, who left the precinct house bleeding after officers jammed a broken broomstick into his mouth and rectum. A few years later, two police shootings of unarmed black men followed, including Diallo in 1999, who was hit 19 times from among 41 police bullets fired after he reached into his pocket for a wallet.
Since then, following police sensitivity training, New York has seen a few killings involving suspects and officers, including last year's shooting of Sean Bell, an unarmed black bridegroom-to-be whom police say they believed was reaching for a gun.
New York now ranks sixth nationwide in the number of police killings, behind Arizona and Illinois, according to Thursday's report.
-Among law enforcement, 380 officers were killed in the line of duty over the three-year period and 174,760 were reportedly assaulted, according to FBI data. Most of the deaths were accidental (221), while 159 were homicides.
-Blacks were disproportionately represented in arrest-related deaths due to alcohol or drug intoxication (41 percent vs. 33 percent for whites); accidental injury (42 percent vs. 37 percent for whites); and unknown causes (46 percent vs. 39 percent for whites).
Mumola said it was unclear why blacks tended to be victims for accidental injuries, which often involve fatalities in the course of a police car chase; or intoxication, which involve overdoses or drunkenness.
-Arrest-related deaths involving tasers or other conducted-energy devices are rising, although overall numbers are low. From 2003-2005, there were 36 such deaths total, with a jump from 3 cases in 2003 to 24 in 2005.
-About half of arrest-related suicides (51 percent) involved attempted arrests for violent crimes. Whites were disproportionately represented in those deaths (57 percent), six times the percent of blacks (14 percent). Hispanics accounted for 26 percent of the cases, and 3 percent involved other or multiple races.
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