In about two-thirds of all rape cases, the victim knows the assailant. According to a Dept. of Justice report "Sex Offenses And Offenders," there is a "remarkable similarity" among rapists: 99 in 100 are male; six in 10 are white; and the average age is the early 30s. Sexual assault offenders are substantially more likely than any other category of offender to have experienced physical or sexual abuse while growing up. About 7 percent of rapes involved the use of a weapon; 2 percent used a gun; 4 percent used a knife.