Former U.S. Rep. Steve Stockman and a former congressional aide were indicted Tuesday by a federal grand jury on 28 charges in a massive scam involving allegations they took hundreds of thousands of dollars from conservative foundations to fund campaigns and cover personal expenses.

Stockman is accused of using two staffers and a series of shell companies to collect more than $1 million in donations under false pretenses, according to court documents.

"The indictment returned by the grand jury today is a significant case alleging serious violations involving use of official positions for personal gain," Acting U.S. Attorney Abe Martinez said. "Violations of the public trust will not be tolerated."

Stockman, 60, of Clear Lake, and his former director of special projects, Jason Posey, 46, formerly of Houston, were charged with mail and wire fraud, conspiracy, making false statements to the Federal Election Commission, making excessive campaign contributions and money laundering.

Another Stockman aide, Thomas Dodd, a former special assistant in Stockman's congressional office, was indicted March 1 and pleaded guilty to his involvement in the same scheme last week.

Read more about the allegations and Dodd's guilty plea: Ex-Congressman Stockman accused of stealing $775,000 from foundations, federal court records say

Stockman and Dodd have been released on bond. Posey had not been arrested Tuesday afternoon, said Jennifer Lowery, a spokesperson for the U.S. Attorney's office.

Stockman has maintained his innocence, blaming his arrest on a "deep state conspiracy." He was arrested earlier this month by federal officials as he attempted to board a flight to the United Arab Emirates at Bush Intercontinental Airport. Prosecutors initially charged him with a criminal complaint describing two counts in the same alleged conspiracy.

"This indictment is not a surprise to Steve," attorney Shaun Clarke said Tuesday. "He remains resolved to fight and he will plead not guilty."

Federal investigators say that between May 2010 and October 2014, Stockman brought in about $1.25 million in donations under false pretenses.

In 2010, Stockman is accused of diverting nearly $285,000 in charitable donations to pay for his and Dodd's personal expenses. He then took another $165,000 in donations in 2011 and 2012 and used most of it to finance his 2012 congressional campaign, according to court records.

Stockman served twice in the U.S. House, once in the 1990s and again from 2013-2015. He then lost a long-shot bid in the Republican primary to unseat U.S. Sen. John Cornyn.

When he took office in 2013 as a U.S. representative for the 36th Congressional District, an area that stretches from the Houston suburbs to East Texas, Stockman and Dodd solicited a $350,000 charitable donation. The funds were then spent on personal and campaign expenses as well as a "covert surveillance project" targeting a perceived political opponent, the indictment alleges.

Stockman Indictment (003) by Lise Olsen on Scribd

In support of the failed senate campaign, Posey is accused of using a nonprofit entity to secure more than $450,000, about half of which was spent on a mass-mailing. Posey used part of the unspent balance to pay for expenses related to the Senate campaign and to fund personal expenses, according to the charges.