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Can you help solve a murder or spot an undetected serial killer?

Open-source website Murder Accountability Project gives the public free access to data about homicide cases from federal, state and local governments, and the FBI.

And there are a lot of them.

More than 211,000 Americans have died in unsolved homicides since 1980, according to The Economist in 2015.

The Murder Accountability Project “is the most complete data on U.S. homicides available anywhere,” the website said.

The database includes two major FBI datasets: The Uniform Crime Report from 1965 to the present and the Supplementary Homicide Report from 1976 to the present.

It also includes data on more than 22,000 homicides that were not reported to the Justice Department that researchers obtained using the Freedom of Information Act.

Anyone can use the site to search for cases based on location, weapon, time frame, and the victim’s sex, age and race, and look for connections or patterns.

“This site is especially useful in cases in which an offender is suspected of killing more than one victim,” the website said. “Possible additional victims may be identified by checking all available reports.”

Authors of the website use the 1996 killing of 6-year-old JonBenet Ramsey as an example.

Ramsey was found strangled in the basement of her Boulder home on Dec. 26, 1996.

“Go to the ‘Search Cases’ tab and locate the SHR report about JonBenet by selecting ‘Colorado’ under state, ‘1996’ by adjusting the year sliders, the exact age of ‘6’ under victim’s age, ‘female’ under victim’s sex, and ‘strangulation’ under weapons. Only one case will pop up,” the site said.

Widen the parameters to see if there were similar killings in Colorado around the same time.

Changing the age to 5-10 and the years to 1980 to the present, one additional case comes up: The rape/homicide of a 10-year-old girl in Colorado Springs in February 1985.

“The 11-year gap between killings suggests a link is unlikely, perhaps, but not impossible,” researchers said.

Widen the search parameters to the entire country and search for cases without an identified suspect.

“[Y]ou will see there were 27 strangulations of young girls reported without an identification of the offender during the last 33 years,” researchers said. “With a few mouse clicks, you can download all of the details of these 27 cases.”

The Murder Accountability Project was founded in 2015 by Thomas Hargrove, a retired investigative journalist and former White House correspondent.

“Every year, at least 5,000 killers get away with murder,” the website said. “In the mid-1960s, police routinely reported clearing more than 80 percent of murders. Today, a department is doing well if it solves 65 percent and dozens of major departments are solving less than half.”