The FBI will continue to resist pressure from legislators and activists for the creation of a fully comprehensive count of all killings by American police officers, the bureau’s director signalled on Monday.



Writing as the FBI released its annual crime statistics, James Comey said an existing voluntary system, under which police departments around the country choose whether or not to submit data on homicides by their officers, will carry on.



Comey said the FBI would try to collect more information – but gave no specific details about how this would be done.

He said of the current information collected: “As helpful as this information is, however, we need more law enforcement agencies to submit their justifiable homicide data so that we can better understand what is happening across the country.”



The FBI counted 444 “justifiable homicides” by law enforcement officers in 2014, according to statistics released on Monday. That total represented a 5.7% decrease from the 471 counted the year before.

Yet both the accuracy of the figures and any trends emerging from them have been called into question due to the voluntary reporting system.



The Guardian is counting all deaths caused by police and law enforcement in 2015, and collecting extensive details on each incident and those killed. As of Monday a total of 871 deaths this year had been recorded by the project, The Counted.



A spokesman for the FBI did not respond to a request for information on how many of the roughly 18,000 law enforcement agencies in the US had submitted data in 2014 or in previous years.



Criticism of the FBI’s system has sharpened since protests erupted last year following the fatal shooting of an unarmed black 18-year-old in Ferguson, Missouri. Mandatory reporting of all homicides by law enforcement was among a series of recommendations proposed earlier this year by Barack Obama’s Task Force on 21st Century Policing.



Senators Barbara Boxer of California and Cory Booker of New Jersey have proposed legislation that would mandate law enforcement agencies to report comprehensive data on the use of deadly force by their officers. Their bill is currently sitting in committee stage, and is presumed to stand little chance of becoming law under the Republican-controlled Congress. Similar legislation has been put forward by Democrats in the House of Representatives.

Boxer told the Guardian on Monday that the FBI was correct to acknowledge the “serious gaps” in its own records, adding that reliable data was pivotal to “understand the scope of this horrific problem and save lives on all sides”.

Democratic congressman Steve Cohen, who reintroduced a bill for national deadly force statistics in January, said the data did not “tell us all we need to know about the use of deadly force by police”.

Cohen has gone on to introduce further proposed legislation to encourage a mandatory independent investigation of officer involved deaths.

Laurie Robinson, co-chair of Obama’s taskforce, described FBI data published on Monday as flawed and unreliable, adding that any potential changes to police practice in the US after nationwide scrutiny accompanied unrest in Ferguson would not have filtered through by the end of 2014.



“I think one has to be very cautious and not read that much into of any of it at this stage,” Robinson said.



“There is a lag in the reporting of the data. The public and professional consciousness on these issues really has occurred in 2015, even though Ferguson occurred in 2014. So I’m not sure that one would expect there would be a dramatic change in behaviour in law enforcement in the last couple of months in 2014.”



Comey said in his statement that the FBI “plan to collect more data about shootings (fatal and nonfatal) between law enforcement and civilians, and to increase reporting overall”. Asked to elaborate, a spokeswoman said: “There’s nothing else we have for you.”



The director said this extra information would be used to create a publication separate to the annual crime statistics that would “outline facts about what happened, who was involved, the nature of injuries or deaths, and the circumstances behind these incidents”.



Robinson said that while Comey’s comments were a welcome rhetorical nod towards better reporting, the FBI director has no power to implement a mandatory reporting program himself.



“What he called for here is exactly right,” Robinson said. “But we’re still at the mercy of having embraced this very, very decentralised state and local law enforcement system. I’m not criticising it; it’s just what we have.”