The sister-in-law of accused Gilgo Beach serial killer Rex Heuermann was left in “profound” disbelief over his arrest for allegedly slaying three sex workers and dumping their bodies on Long Island, according to a report.

Dr. Johanna Ellerup, the half-sister of Heuermann’s estranged wife Asa Ellerup, shared her “stunned” reaction to the charges against her brother-in-law in a statement to NBC NBC News, where she also said she’s incredulous over failing to recognize a sinister side to the alleged killer.