The paper said that during the first five months of this year, 385 people – more than two a day – were killed.
The number of black people was disproportionately high among the victims, especially unarmed ones.
Official statistics rely on self-reported figures from law enforcement agencies.
They suggest about 400 people have been killed each year since 2008.
The US has seen a number of controversial cases where unarmed black people have been killed by white police officers.
Police are allowed to use deadly force when they fear for their lives or the lives of others, however there is currently no reliable way of tracking police shooting deaths.
Instead, the government relies on self-reported figures from the nation’s 17,000 law enforcement agencies. The figures exclude killings deemed not to have been justified.
It found a homicide rate of almost 2.6 per day so far this year – more than double the average 1.1 deaths per day reported in FBI records over the past decade.
“These shootings are grossly underreported,” former police chief Jim Bueermann told the newspaper. “We are never going to reduce the number of police shootings if we don’t begin to accurately track this information.”
Among the report’s other findings:
- Black people were killed at three times the rate of whites or other minorities when adjusted for local population
- Most were armed, but one in six was unarmed or carried a toy weapon
- 365 men and 20 women were killed
- Most (118) were aged 25-34, while 94 were 35-44. Eight were children younger than 18
- In all three 2015 cases in which charges were subsequently filed against police officers, videos had emerged showing officers shooting a suspect during or after a chase on foot.