The number of murders in Oklahoma reached a two-decade high last year, according to new data released by the Oklahoma State Bureau of Investigation, a rise that mirrored the national trend. Homicides in the U.S. in 2020 increased nearly 30% over the previous year, the largest one-year jump since the FBI began keeping records. The O.S.B.I. tallied 287 murders in Oklahoma last year, or a 15% increase over 2019.