A police press conference in the US about a serial killer case took a bizarre turn when a woman posing as a sign language interpreter started making unintelligible gestures.

While Tampa police chief Brian Dugan shared crucial information about the high-profile case before the media in the Floridian city, Derlyn Roberts stood to his right and waved her arms about "like she was singing Jingle Bells", according to one sign language expert.

Rachelle Settambrino, a sign language professor at the University of South Florida, said: "A lot of them were invented signs. I wasn't able to understand anything she was saying."

SCREENGRAB According to one sign language expert, Derlyn Roberts "waved her arms around "like she was singing Jingle Bells".

According to Settambrino, during the press conference Roberts signed the following: "Fifty-one hours ago, zero 12 22 (indecipherable) murder three minutes in 14 weeks ago in old (indecipherable) murder four five 55,000 plea 10 arrest murder bush (indecipherable) three age 24."

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To make matters worse, the deaf mother of one of the victims was in attendance.



Tampa Police Department spokesman Steve Hegarty took responsibility for the mistake, saying he assumed Roberts was a contractor from a company the department used and "didn't ask enough questions".

The mistake has angered many in the deaf community, with Settambrino saying she was "disappointed, confused, upset" by the security lapse.



Roberts, meanwhile, is yet to explain why she performed the baffling act, which police have admitted was more of an ethical violation than an actual crime.



The 53-year-old has previously been arrested for fraud, and has one conviction.

The incident brings back memories of impostor Thamsanqa Jantjie, who grabbed headlines around the world when he stood for hours alongside global leaders and made "childish hand gestures" during the memorial service for former South African President Nelson Mandela in 2013.