Washington - The head of the Internal Revenue Service refused to apologize Friday for lost emails in the scandal over the improper screening of conservative groups and denied more widespread computer failures.

House Ways and Means Committee Chairman Dave Camp, R-Mich., grilled IRS Commissioner John Koskinen about why Congress wasn't informed earlier that a computer hard drive failure had compromised Lois Lerner's email records. She headed the exempt organizations division that acknowledged last year inappropriate scrutiny of tea party groups.

"I have never seen an IRS so broken," Camp said in his opening statement, adding that average Americans find it hard to believe that the never-popular tax-collecting agency can just lose records. "How far would the excuse of, 'I lost it,' get with the IRS?"

Camp asked for an apology for being kept in the dark about the hard drive failure.

"I don't think an apology is owed," snapped Koskinen, a management turnaround specialist tapped by three presidents to fix troubles in government.

At times, the contentious hearing lost all decorum.

"I don't believe you. That's your problem, no one believes you," Rep. Paul Ryan, R-Wis., told Koskinen.

Rep. Kevin Brady, R-Texas, called the agency Koskinen leads "the most corrupt and deceitful IRS in its history."

Koskinen, sworn in two days from Christmas last year, was taken aback.

No one has ever questioned his integrity, he countered, noting the agency has a long history. That was a not-so-veiled reference to President Richard Nixon, whose misuse of the IRS against opponents became one of the articles of impeachment that forced Nixon to resign.

Republicans argue that's not far off from the unfair treatment of applications by conservative organizations for tax-exempt status. The IRS maintains the scrutiny was to ensure the groups in question were educational organizations, not political ones funneling money into campaigns.

The central focus Friday was when Koskinen knew about missing emails and when he decided to tell Congress about them. Camp and other top Republicans argue that the Treasury Department and the White House were aware of the hard drive failure in April, yet the IRS told Congress on June 13.

Koskinen tried to explain that in fact this information already had been provided to Congress, that lawmakers were told back in March that the date sequence of emails suggested something was awry.

Koskinen said he was unaware of communication between his legal department and other branches of the federal government. In any event, he insisted, it didn't affect anything the IRS was doing.

As to lost emails, Koskinen disputed the term, saying about 24,000 have been recovered from accounts to which Lerner had emailed. By the end of the month, 67,000 Lerner emails will have been provided to Congress.

"A hard drive crash does not mean the emails are lost forever," the IRS chief said.

It was Lerner, he added, who pushed her information technology department to try to recover lost emails in April 2011. The effort was eventually pushed up to the criminal division of the IRS, which has high-level forensic specialists trained in recovering lost data. They could not recover any data.

A backup tape designed to store IRS emails only does so for six months - industry practice - and the missing emails from a period between 2009 and 2011 disappeared from IRS computer servers. It wasn't clear whether the email of IRS executives is stored differently than that of the roughly 90,000 rank-and-file IRS employees.

Taking responsibility for the decision to delay the release of information to Congress, Koskinen said the delay was meant to provide more complete information to lawmakers.

"If we provide incomplete information, people sometimes tend to leap to a conclusion," he said.

Asked if he supported a special prosecutor, Koskinen said there are six government investigations now underway and a special prosecutor would be a "monumental waste of taxpayer money."