The witness testified against Leon De St Aubin, who was convicted of an execution-style shooting outside Wandsworth prison.
Two months after he was found guilty his girlfriend, Lydia Lauro, 33, got a civilian job at Hammersmith Police Station in west London.
She plied Hayden Cheremeh, a fellow police detention officer, with s3xual favours and used his log-in to get into the intelligence system.
Lauro then handed the details of a protected anonymous prosecution witness to Aubin while he was behind bars.
She and Cheremeh, 36, were jailed for five years each at the Old Bailey on Friday.
Lauro did not show any emotion as the sentence was passed.
Cheremeh refused to attend court .
Judge Anthony Morris said Lauro also used the database to lookup the details of people in custody at Hammersmith police station "in order to find sexual partners for yourself".
She leaked the details of a young woman who had given crucial evidence from behind a screen, using a voice-altering device and under a pseudonym.
Lauro seduced Cheremeh to get his access to the system and looked up more than 150 confidential reports while trying to track down the witness.
She sent screenshots of a list of possible names of the witness to Diana Lank, the mother of Aubin's codefendant.
Lank, a wealthy businesswoman who ran a clothes shop in Chelsea, masterminded the plot after the witness testified against her son Rupert Ross.
She admitted receiving the confidential information but claimed her actions were justified, insisting her son had been wrongfully convicted.
Judge Morris described her as "forceful and manipulative".
Laurie-Anne Power, defending Lauro, said her client was misguided, vulnerable and had been influenced by Ms Lank.
Cheremeh, a former police community support officer, was totally obsessed with Lauro.
Jeminipe Akin-Olugbade, defending, described him as a "naive, infatuated and possibly over-idealistic person who got caught up in actions far greater than himself".
Cheremeh and Lauro were found guilty after trial of conspiracy to commit misconduct in public office between November 2011 and May 2013.
Lank was cleared of the same charge after the jury failed to agree on a verdict against her.
Aubin and Ross were handed a minimum term of 30 years in November 2011 for the shooting of Darcy Austin-Bruce.
Dulwich College ex-pupil Ross was from a wealthy background, with some of his family working as lawyers, but fell under the spell of drugs.
He shot Mr Austin-Bruce, 20, five times outside the jail in May 2009, before Aubin drove him away on a stolen moped.