Sen. watchdog head denies allegation he hired prostitutes . Senate Ethics Committee group that surfaced allegations now questions tipster 's credibility . Tipster `` watchdog head wo n't talk directly to investigators , Peter Williams '' says . Watchdog wo n't confirm whether it is investigating .
Sen. Robert Menendez denies allegation he hired prostitutes . Watchdog group that surfaced allegations now questions tipster 's credibility . Tipster `` Peter Williams '' wo n't talk directly to investigators , watchdog head says . Senate Ethics Committee wo n't confirm whether it is investigating .