Who is Croft from The Pelican Brief and what is their importance?

Croft is paroled drug offender who once takes photographs for the Washington Post but now freelances as a sleazy "halfass private investigator," Croft likes to work for Grantham, who does not pretend to be pious when he needs dirt. Grantham lends Croft his Volvo to stake out the phone booth from which an anonymous tipster, Garcia, has called earlier. Croft shoots two rolls in two minutes. Memorizing the face, Croft then goes morning, noon, and night to the courthouse to look for Garcia and, on another tip, to the offices of White and Blazevich, where he spots his man. By this point, if he had other clients, he would tell Grantham to forget the boring gig.