I just happened upon this today... an old case (1985) where the abductor/killer (Larry Gene Bell) made harassing phone calls to the victims' family. Bell was put to death (electrocution) in 1996.
"While Shari was still missing, someone identifying himself as Shari's abductor made the first in a series of harassing phone calls to the Smiths.   Because the caller knew details that would have been known to only Shari or her kidnapper, the Smiths made notes of the calls.   Authorities eventually traced and recorded all later calls.   During the first conversation, the abductor told Shari's family they would be receiving a letter from Shari.   State officials intercepted her letter, entitled “Last Will and Testament,” from the mail.   Apparently, her abductor had Shari draft it shortly before her death.   On June 5, 1985 the caller-later identified as Bell-provided directions leading to Shari's body.   Unfortunately, by the time Shari's body was located, the pathologist could not ascertain either the cause of her death or whether or not she had been sexually assaulted.   The pathologist believed, however, that Shari either suffocated or died from dehydration (resulting from a rare form of diabetes from which Shari suffered).
Following the discovery of Shari's body, Bell made harassing phone calls to the Smiths for the next three weeks.   During these calls, Bell callously depicted how he abducted Shari at gun point, raped and sodomized her, wrapped her head in duct tape, and suffocated her.   He even malevolently discussed Shari's funeral arrangements with Shari's sister.   In one call, Bell identified the location of the body of ten-year-old Debra May Helmick, a little girl he kidnapped exactly two weeks after he kidnapped Shari."
http://caselaw.findlaw.com/us-4th-circuit/1307072.html
AND here it mentions he often spoke with the victims' sister (which makes me wonder if this was coincidence):
"Throughout the largest manhunt in South Carolina history, Bell made eight telephone calls to the Smith family,
often speaking with Shari's sister, Dawn. Bell eventually gave exact directions to the locations of both of the bodies and described to the family how he had killed Smith."
https://en.wikipedia.org/wiki/Larry_Gene_Bell