The investigation into the election campaign of Wisconsin Gov. Scott Walker appears to be heating up. A Walker contributor was jailed Tuesday night after refusing to cooperate with a prosecutor investigating possible campaign law violations.

Andrew Jensen, a real estate broker, was arrested as part of a lengthy secret probe by Milwaukee County prosecutors into Walker's 2010 campaign for governor. No charges have been filed, according to a sheriff's spokesman.

Jensen was arrested because "he wouldn't adopt their [prosecutors] version of events," his attorney, Patrick Schott, told the Milwaukee Journal-Sentinel.

FBI agents raided the Madison home of a former high-ranking Walker aide in September and removed documents. Walker has insisted he did nothing wrong. Several Walker aides, including his press secretary, have already been granted immunity in return for their cooperation.

The investigation into whether Walker allies improperly did campaign work using Milwaukee County government computers and phones is underway just as the campaign to recall him from office is gathering steam. Walker opponents say they have more than half the 540,000 ballots needed by Jan. 17 to force a recall election.

The Republican governor generated a firestorm when he pushed through controversial legislation stripping state employees of union bargaining rights.