Bill Cosby, seen here at an August court appearance, is set for a retrial on sexual assault charges in April, after his first trial last spring ended in a hung jury. (Matt Rourke/AP)

The prosecutor in the Bill Cosby case asked a Pennsylvania judge to allow testimony from 19 alleged prior victims of the entertainer, whose retrial on sex assault charges is set to begin April 2.

The request is the first public indication of the shape and parameters of the prosecution case, and it represents a significant expansion of the government's effort to portray Cosby as a serial predator. When Cosby was tried in June, prosecutors sought to include testimony from just 13 women who said they had been assaulted by the comic legend.

But it remains to be seen how this latest move by prosecutors will play out: Last year's effort by prosecutors to introduce so-called "prior bad acts" testimony was largely unsuccessful, as the judge allowed only one of the 13 to appear at Cosby's trial, which ended with a hung jury.

In their request Thursday, prosecutors said that Cosby "has spent a lifetime entertaining audiences in front of the camera. Off camera, he has followed and, indeed mastered, a more nefarious script — a victimizing sexual script. . . . To satiate his desire, he has engaged, over the course of a lifetime, in a pattern of serial sexual abuse."

Courts are often reluctant to allow testimony from alleged prior victims. But in Pennsylvania, the courts have allowed such testimony in instances in which the testimony could be used to establish a clear pattern of behavior.

The prosecution request includes Kelly Johnson, an assistant to Cosby's personal-appearances agent who delivered emotional testimony, sobbing on the witness stand as she said that the entertainer gave her pills that left her woozy and unable to see clearly before she says he sexually assaulted her.

"I remember wanting to cover myself and not being able to," Johnson testified about the alleged incident in 1996 at the upscale Hotel Bel-Air in Los Angeles.

The rest of the alleged victims are not identified by name. But 12 of the alleged prior victims included in the new prosecution request were rejected as witnesses last spring by the Montgomery County, Pa., judge overseeing the case, Steven O'Neill. However, the request includes six new potential witnesses. The full list includes flight attendants, aspiring models and a performer who was the opening act for a Cosby comedy show.

Cosby faces felony charges for allegedly drugging and sexually assaulting Andrea Constand, a former Temple University employee, at his suburban Philadelphia estate in 2004. Cosby, now 80, has denied sexually assaulting women.