The bribery and tax fraud investigation, kept under wraps for 10 months and made public on Tuesday, when 22 senior officials and businessmen were brought in for questioning by the National Fraud Squad in Bat Yam, could well prove to be the most damaging case of corruption in high places in recent years, and that's against very stiff competition. "This time it's not just politicians - we know they're all dirty. It's one of us now," said a shocked Treasury official after learning that Tax Authority Director Jacky Matza and his predecessor, Eitan Rub, had both been arrested on suspicion of taking bribes. The official wasn't exaggerating. These are not a couple of crooked planning officials in some local authority turning a blind eye to a balcony without a permit or traffic cops taking a bribe. Rub and Matza headed one of the state's most important financial institutions, one that has its hands in the pockets of every working person. If only a third of what the police are saying is true, it will be difficult to trust any level of the Treasury, traditionally the most professional and least politicized branch of Israel's civil service. Their arrest made this police operation a trifecta - corruption on three sides: private business, politics and senior officialdom. The political side is also special this time. Shula Zaken, questioned over suspicions she was the go-between, might not be an elected representative but she is nonetheless an intensely political creature. For almost three decades she has gone wherever Ehud Olmert has, from his law firm to the Knesset, the Health Ministry, Jerusalem City Hall, the Trade Ministry and the Treasury, and now she is the gatekeeper at the summit of power in the Prime Minister's Office. The longest serving of all Olmert's advisers, Zaken is the one who holds his cellular phone for him, remembers all his appointments and knows who he meets. But Zaken is much more than a super-secretary; over the years she has become a political operator in her own right, with the backing of her boss and of a network of family members and friends in the Kurdish community. She watched Olmert's back in the vicious world of local Jerusalem Likud politics. Over the last few months, when the Shin Bet (Israel Security Agency) prevented Olmert from attending matches of his beloved Betar Jerusalem for security considerations, Zaken took his place in the VIP box, where local political deals are closed. Three of the businessmen arrested on suspicion of bribing Rub and Matza are integral parts of Zaken's world: her brother, Yoram Karshi, a member of the Jerusalem City Council; contractor Simo Toboul, a close friend; and Kobi Ben-Gur, a former owner of Betar. All three are prominent Likud activists. Ben-Gur was No. 22 on the Likud's Knesset list in the last election. The breadth of Zaken's connections, Olmert's reliance on her and the fact that she sits at the central junction of power in Israel render her more influential than some ministers and the allegations against her all the more serious. No one has suggested that Olmert was aware of his old secretary's alleged dealings, but even if he is never questioned in the case, it could be deeply damaging. If the case against her proves strong, Zaken will have to leave her post at least temporarily, depriving Olmert of one of his most trusted lieutenants in one of his most vulnerable periods.