Prosecutors yesterday hammered home to jurors in the fraud trial of former Allegheny County Coroner Dr. Cyril H. Wecht a central theme of their case, that he routinely billed private clients for inflated airfare and limousine rides he never took.

Dr. Wecht's former administrative assistant, Eileen Young, who was on the witness stand for a third day under a grant of immunity from prosecution, took the blame for billing clients for the phantom limousine rides.

Ms. Young, the top administrative assistant at the Allegheny County coroner's office from 2002 to 2005, also was paid separately for handling Dr. Wecht's private business.

She testified during the 12th day of trial that she knew Dr. Wecht never took the limousine rides she billed to clients at $80 or $90 per round trip.

Instead, other witnesses have testified, Dr. Wecht would drive to the airport with a deputy coroner, who was responsible for taking the county vehicle back to Pittsburgh.

Ms. Young said she was "ashamed" for what she did, going so far as to change her handwriting on the round-trip limo receipts to make it appear that both portions were filled out by chauffeurs on different days when, in fact, she filled them out at the same time on a pile of blank receipts she kept in her desk.

Ms. Young said she adopted the practice from her predecessor, Maribeth Blettner, who was Dr. Wecht's assistant for 31 years.

Ms. Young said Dr. Wecht was aware of the fake billing -- she added that "his justification made very good sense to me," although she was not asked what she meant -- but he did not know she altered her handwriting.

"I don't always make the best decisions," Ms. Young said.

"Did it ever strike you, Ms. Young, that was a way, a practical means of deceiving your clients?" Assistant U.S. Attorney James Wilson asked.

"Yes," she answered. "I followed suit. I'm ashamed to admit I realized what I was doing. Nobody made me do it. I felt that Dr. Wecht was worth it, and I'm sorry. I'm not perfect."

With that, she shrugged her shoulders.

Asked about increasing the fake round-trip limousine charges to $90 from $80 in early 2002, Ms. Young took credit for the idea in a conversation she had with Dr. Wecht about raising his fees for private clients.

"I said, 'Dr. Wecht, you've been charging $3,500 for a long time and your limo charge has been the same for a long time, and I think maybe we should look at raising them,'" Ms. Young testified. "I had said I thought that this was low. I don't know what limo fees are. I don't really go in a limo. I just suggested maybe we should raise that slightly, too."

Mr. Wilson spent much of the afternoon showing Ms. Young numerous invoices she sent to Dr. Wecht's private clients -- including Exxon Mobil Corp., the Church of Scientology and a Jewish center in Florida -- that overcharged for airfare, sometimes by more than $1,000.

"If you travel 30 times a year, that starts to add up, doesn't it," Mr. Wilson asked in one of several exchanges with Ms. Young that drew objections from the Wecht defense team.

Mr. Wilson hardly missed an opportunity to mention the fake limo bills and the fact that Dr. Wecht never used the service.

The only explanation Ms. Young provided was that she used figures for airfare on the invoices provided by either Dr. Wecht or his private secretary, Florence Johnson, which were based on quotes they received from US Airways instead of the actual ticket price.

Ms. Young said she never reconciled the amounts she billed private clients with the actual expenses incurred on the American Express statements she received on behalf of Dr. Wecht. She also said she never recalled Dr. Wecht alerting her that he had overcharged or undercharged a client and asking her to modify an invoice as a result.

"Did the defendant, after examining the invoice, ever come back to you and say, 'Oops, Eileen, it looks like we overcharged this guy by almost $300?'" Mr. Wilson asked after one example. The answer was no.

In detailing some of the alleged overcharges, the government said invoices to private clients charged $98 for one round-trip ticket and $246.40 for another.

However, based on credit card receipts, Dr. Wecht really paid only $110 for a single round-trip ticket covering cases in Philadelphia and New York in 2001.

"Can you account for how two separate invoices were prepared for what appears to be one round-trip airfare?" Mr. Wilson asked Ms. Young.

"No," she replied.

In another case, the government contended, Dr. Wecht charged a client $1,335.50 for a round-trip ticket between Pittsburgh and Tampa, Fla. that really cost him $153.70 for a one-way trip.

In a third case, the government said, Dr. Wecht charged Exxon-Mobil for a $695 round-trip ticket to a 2002 speaking engagement in New Jersey -- one in which he made sure to note in a letter to the company that he enjoyed the chocolate chip cookies they gave him.

However, Mr. Wilson contended, records showed that Dr. Wecht actually got a $347.30 refund from US Airways that was apparently never passed along to his client.

Dr. Wecht is charged with 41 counts of mail fraud, wire fraud and theft from an organization receiving federal funds. Trial resumes today with Ms. Young still under direct examination.