"I also want to be clear that our investigation does not exonerate Darren Wilson," Bell said on Thursday as quoted by the WICS/WRSP local broadcaster. "The only question is whether we can prove beyond a reasonable doubt that a crime occurred. The answer to that question is 'no,'"
Last August, the victim's father, Michael Brown Sr., urged prosecutors to reopen the case against former Ferguson police officer, Wilson, who shot and killed the unarmed 18-year-old Michael Brown during a confrontation on 9 August, 2014.
As a result of the five-month investigation that ended a few weeks ago, Wilson will not be charged in Michael Brown's death.
The killing of Michael Brown by police sparked weeks of protest in the St. Louis suburb of Ferguson, which intensified after a grand jury decided not to indict Wilson.
Brown’s death also contributed to a growing debate in the United States over the use of excessive force by police throughout the country as well as racism.