GREENSBORO, N.C. - John Edwards' former aide acknowledged Thursday that much of nearly $1 million in campaign supporters' cash went to build his North Carolina dream house, not to buy the silence of the presidential candidate's pregnant mistress.

Andrew Young testified for a fourth straight day at Edwards' campaign finance fraud trial, peppered with questions from Edwards attorney Abbe Lowell about the money from two donors that flowed into personal accounts controlled by Young and his wife.

Young has said he took secret payments from wealthy donors at Edwards' direction to help conceal the presidential contender's affair with Rielle Hunter and keep his 2008 presidential campaign viable.

Young said the checks secretly provided by a then-96-year-old heiress were mixed with the couple's other funds as they built their $1.5 million hilltop house on 10 acres near Chapel Hill, N.C. Young often deferred questions on the payments to his wife, Cheri, saying "my wife is the one who handles the finances in our family."

Young's testimony is considered key to the prosecution's case that while campaigning for the White House, Edwards directed a scheme to use the money from the heiress and a Texas lawyer to conceal his affair with Hunter.

Young initially claimed he was the father of Hunter's daughter and took her into his home with his wife.

Lowell asked Young about numerous changes to the construction of the North Carolina house after the payments started coming in, including a pool, home theater, and extra bedroom.

At the time, Young and his wife were living with Hunter in a rental mansion along the California coast, paid for by a wealthy lawyer who served as Edwards' campaign finance chairman.

"We were living out in Santa Barbara and we lost our sense of perspective," Young said on the witness stand. "The house became more and more extravagant."

Edwards denies knowing about the $725,000 in checks from heiress Rachel "Bunny" Mellon sent to Young through her interior designer. In addition to the maximum $2,300 to the Edwards campaign allowed by law, Mellon also provided $6.4 million to a political action committee and anti-poverty foundation tied to Edwards.

A second pool of money at issue in the case involves $200,000 given by the wealthy lawyer, Fred Baron. Records presented at trial show Baron paid for private jets, five-star hotels, and other expenses incurred by Hunter and the Youngs. Baron died in 2008 of cancer at age 61.

Young testified Thursday that he had sent Baron an invoice for many of the expenses the aide had already paid for with money from Mellon; he said Baron then wired an additional $325,000 to the builder of the Youngs' house.