By Joseph Ax

NORRISTOWN, Pa. (Reuters) - Bill Cosby returned to a Pennsylvania courthouse on Tuesday for the first time since his lawyers' failed effort to have the sexual assault charges against the comedian thrown out.

Striding past dozens of television news cameras, Cosby, 78, headed to the courtroom where prosecutors in Montgomery County are expected to outline some of the evidence against him.
Before being hit by a wave of sex assault allegations, Cosby had been one of the most beloved U.S. entertainers.

A heavy police presence was aimed at keeping order outside the courthouse in Norristown. Tuesday's preliminary hearing will focus on the only allegation that has led to criminal charges, that Cosby in 2004 drugged and assaulted Andrea Constand, a former basketball coach at his Temple University alma mater.

Cosby has denied ever assaulting anyone and has portrayed his encounter with Constand as consensual.

The vast majority of the sexual assault accusations by about 50 women dating back to the 1960s are too old to be the subject of criminal prosecution. Pennsylvania prosecutors leveled their charges in December, days before the statute of limitations was to expire.

Several cases are the subject of civil lawsuits, in which victims say Cosby libeled them when he accused them of lying about the incidents.

The accusations have destroyed Cosby's reputation, which he built during years of family-friendly comedy.

Last month, an appeals court rejected a bid from Cosby's lawyers to have the criminal case dismissed because of what they described as a non-prosecution agreement he struck with a former Montgomery County district attorney a decade ago.

The former prosecutor, Bruce Castor, has said he agreed not to press charges in exchange for Cosby's testimony in a civil lawsuit filed by Constand.

But current prosecutors questioned Castor's testimony, saying there was no written evidence of such a deal. They also said Castor did not have the legal authority to prohibit his successors from bringing charges in the future.

(Reporting by Joseph Ax in Norristown, Pa.; Editing by Barbara Goldberg, Scott Malone and Lisa Von Ahn)