A prosecutor has attacked US star Bill Cosby’s defense witness, claiming her testimony was “fictional”.

Stewart Ryan rounded on Marguerite Jackson, a Temple University academic adviser who testified that Cosby’s chief accuser, Andrea Constand, once spoke of falsely accusing a high-profile person of sexual assault so she could file a lawsuit.

He called it a “fictional conversation”.

Mr Ryan also rejected the defence explanation that the 80-year-old US star paid nearly 3.4 million dollars (£2.4m) to settle Constand’s civil lawsuit in 2006 because it was a nuisance and he feared bad publicity.

Cosby is charged with drugging and assaulting Constand at his home outside Philadelphia. He says their sexual encounter was consensual. His lawyers say Constand framed him so she could file suit.

Prosecutors said the star used his good-guy image as America’s Dad to gain unsuspecting women’s trust before knocking them out with powerful drugs and violating them.

Delivering closing arguments Kristen Feden said Cosby is “nothing like the image that he played on TV”.

She said Cosby led a secret life that ran counter to the wholesome image he projected as Dr Cliff Huxtable on his top-rated 1980s sitcom.

The star’s wife of 54 years was in the courtroom for his lawyers’ arguments.

They urged a jury to acquit the star claiming the charges are based on “flimsy, silly, ridiculous evidence”.

They branded Constand a “pathological liar and highlighted more than a dozen inconsistencies in what Constand has said over the years about her relationship with Cosby and her allegations that he drugged and molested her at his suburban Philadelphia home.

The jury is expected to get the case later Tuesday.