WASHINGTON—While reviewing expense reports for a 2000 construction project, a bookkeeper for Alaska oil services giant VECO Corp. asked for an explanation. Who was this work for, she asked? Why was it performed?

The cryptic note she received back included the instruction, “No paper trail.”

Federal prosecutors say the note, introduced as evidence Friday at Sen. Ted Stevens’ corruption trial, was part of a scheme by Stevens and VECO founder Bill Allen to conceal more than $250,000 in home renovations and other gifts that the contractor bestowed on the Senate’s longest-serving Republican.

Bookkeeper Cheryl Boomershine testified Friday that VECO employees submitted invoices and expense reports for a project located in Girdwood, a ski town south of Anchorage where VECO didn’t normally work.

When she requested details, she said she got little information back. The note listed only one reason for the secrecy: “per Bill Allen.”

The unusual project was a dramatic renovation of Stevens’ home and it has become the centerpiece of his gift-giving trial. Prosecutors say he withheld the free renovations from his Senate disclosure forms.

The 84-year-old Stevens, a Senate powerhouse for generations, has seen both his influence and re-election prospects weakened by the case. His lawyers say he was a busy senator who couldn’t oversee every aspect of the project but who, like every homeowner, paid the bills that came in—$160,000 in all.

But VECO employees testifying Friday painted a picture of a project that was far from normal. They described being pulled off their regular jobs and being dispatched to the senator’s house.