Murder Wave of the 70's Appears to Ebb in Cities
First reports from police depts in 12 selected major cities show that in 9 of them the number of homicides dropped markedly and in some cases sharply, in 1975, after reaching a peak in '74; statistics on cities selected; chart compares murder rates in selected cities, '74 and '75 and compares homicide rate per 100,000 population for same periods (L)