Clinton condemns 'cowardly' killing
She strongly condemned the murder as senseless and applauded the efforts of police to bring the perpetrators to justice.
"There is no justification for this outrageous and cowardly act," she said.
"I offer my sincere condolences to the family, friends and colleagues of officer Black, who had a long and distinguished record of service.
Three men have been arrested by police investigating the shooting.