By a Staff Reporter : Former Mumbai police chief Param Bir Singh, who has been implicated in four extortion cases, appeared in the office of City Police's Crime Branch Unit 11 on Thursday morning.He arrived in Mumbai after 231 days.He had been missing since October.Many thought he had fled from the country.Although he was in Chandigarh.On Monday, the Supreme Court granted him protection to avoid arrest.The supreme court had asked him to join the probe into allegations of extortion chartge against him.