recorded since tracking began in the 1960s. the number spiked in the summer of 2020 the fbi report says, and then remained elevated for the rest of the year. why? >> there was a pandemic, and then we had increased street protests in connection with, as a reaction to the death of george floyd at the hand of a minneapolis police officer and similar kinds of cases. >> reporter: another possible factor experts say, after incidents of police brutality like the george floyd murder, more police officers may have retired or become reluctant to get involved in altercations, and the public less likely to trust them. another reason? more gun violence. last year, when gun sales skyrocketed, the fbi says 77% of the reported murders were committed with a gun. that's up three points from 2019 and up 10% from a decade ago. >> it's probably a greater availability of guns. some commentators have suggested that people used their stimulus check to purchase a gun.