A man arrested for investigation of armed robbery and rape may be responsible for as many as 20 holdups in the Hollywood-Rampart area, Los Angeles police said. Oscar Rodriguez, 27, was arrested last week in the robbery and sexual assault of a 32-year-old Eagle Rock woman, Detective Sam Jacobellis said. The woman was robbed, along with three companions, in the 3600 block of Eagle Rock Boulevard. The woman was then taken to an isolated, hilly area where she was raped, he said. During the search for Rodriguez, officers discovered that he may have been involved in a series of armed robberies in the Hollywood and Rampart areas in which he posed as an undercover police officer, Jacobellis said. Rodriguez was booked and remained jailed for investigation of 11 felony counts of robbery and sexual assault.