Sometimes dry and at other times eye-opening, federal prosecutors have spent the first four days of an Atlanta City Hall corruption trial building the foundation of their bribery case against former city of Atlanta official Pastor Mitzi Bickers.

So far prosecutors have gone into the weeds with witnesses into how contracting at the city is supposed to work. They’ve chronicled the flurry of deposits, cash and wire transfers with Bickers and two private contractors allegedly involved in the scheme, as well as when the two businessmen received city business.

And prosecutors also have revealed Bickers’ apparent preference for spending cash to finance her lifestyle, including the purchases of a $775,000 lakefront home, a luxury SUV and jet skis.

Bickers, a political consultant who helped Kasim Reed win his first run for mayor in 2009 and pastor of Emmanuel Baptist Church, is accused of orchestrating a cash-for-contracts plan involving Elvin “E.R.” Mitchell Jr. and Charles P. Richards Jr., who won some $17 million in city business from 2010 to 2014.

Bickers did not have a direct role in contracting, but prosecutors allege she had clout at City Hall because of her work helping Reed get elected.

But not everything has gone off without a hitch. A key witness in the case, Cotena Alexander, a current city employee who Assistant U.S. Attorney Jeffrey Davis identified in the first day of trial as someone who took bribes to help Bickers steer city work, began the trial as an apparent cooperating witness.

Since opening statements last week, she now appears to have had a change of heart and has informed prosecutors she won’t cooperate if called to the stand.

Alexander’s decision to assert her Fifth Amendment right against self-incrimination led Bickers defense team to seek a mistrial on Tuesday, which U.S. District Court Judge Steve C. Jones denied. Losing Alexander, if she ultimately does not testify, could hurt the prosecution’s ability to connect Bickers to alleged bid steering that occurred after Bickers left her City Hall job in 2013.

Here are some of the highlights through four days of testimony:

Money movement

Much of the first few days have been spent outlining the series of transactions between Mitchell, Richards and Bickers and her companies and associates. Richards, who pleaded guilty and is a cooperating witness, testified to sending “marketing money” to Mitchell that he said went to Bickers and that sometimes Richards paid directly to the pastor. Sometimes those funds were paid before contracts were awarded, but mostly they were in the form of kickbacks after work was awarded, Richards testified.

The defense has argued that Richards did not have direct knowledge that money he sent to Mitchell went to Bickers to influence contracts. Richards said it was possible but unlikely given that the contractors kept winning city work even when they weren’t the lowest bidder.

Former girlfriends of Bickers testified to the pastor’s constant use of cash to fund her lifestyle, as well as the incorporating of businesses and opening of bank accounts in their names. One testified that Bickers seemed to spend little time at her $57,000-per-year city job.

On Monday, the government concentrated on Bickers’ June 2011 purchase of her Henry County lake house and how she came up with some $300,000 in nine days to fulfill the sales agreement. An auditor for the U.S. Attorney’s Office testified Bickers received more than $500,000 in income during the first six months of the year, but only about $16,000 of that came from her city job. Most came in the form of cash deposits or wires from the contractors.

On Tuesday, a retired top sales official at a metro Atlanta motorsports vehicle dealership testified about Bickers buying jet skis and an all-terrain vehicle. And the general manager of a car dealership testified about Bickers purchasing a $46,000 GMC Acadia Denali in 2014.

Bickers’ taxes:

A city of Atlanta employee who runs a side business as a tax preparer testified on Tuesday she helped file Bickers tax returns in 2009, 2010 and 2011. She said Bickers provided all tax documents to her and claimed no outside business income. In 2010 and 2011, Bickers claimed about $50,000 and $57,000 a year, respectively, in city wages and received tax refunds.

Prosecutors have alleged Bickers collected hundreds of thousands of dollars from the two contractors in those years.

The defense attempted to seed doubt by showing the tax preparer, who once worked for the IRS, is not a certified public accountant. She also did not sign one of Bickers’ tax returns as a preparer.

Contracting norms bypassed:

In 2011, Mitchell received more than $1 million from the city for snow removal work in the wake of a brutal winter storm. In the wake of that storm, which caught Atlanta unprepared, the city contracted with five companies to be emergency on-call vendors to respond to future severe weather.

Those five companies did not include Mitchell’s company, Cascade Building Systems. But in 2014, during a pair of winter blasts, including the infamous Snowjam storm that left motorists stranded across the metro area, Mitchell’s company was awarded the most city business of any contractor.

Witnesses testified Mitchell was paid more than $5 million to buy salt and remove snow and debris. He also charged prices for salt, labor and equipment that were far higher than the pre-negotiated rates of the five approved vendors.

Former Commissioner of Public Works Richard Mendoza and Rita Braswell, an administrative program manager in the public works department, testified this week that even though they suggested other companies address the 2014 storm, Cotena Alexander continued to steer contracts to Mitchell.

Some of the companies on the approved list were contacted to remove snow as a second storm hit several days later in February. But they never were called into duty, company representatives said in testimony.

A witness to plead the Fifth:

Though Cotena Alexander’s name has come up in testimony and prosecution exhibits, it now appears she will not cooperate in her testimony.

That means the jury won’t hear her questioning by prosecutors, nor would the defense be able to cross-examine Alexander.

Prosecutors allege Alexander helped Bickers funnel contracts to Mitchell and Richards after Bickers left City Hall in 2013. Davis, the assistant U.S. attorney, said in his opening statement that Alexander used money provided to her by Bickers to buy personal items and pay off $30,000 in debt.

It’s unclear if Alexander had previously reached an agreement with prosecutors in exchange for her testimony or if she faces any legal jeopardy. After her name came up in the prosecution’s opening statements last week, Alexander was placed on administrative leave from her current city job as deputy commissioner for the Atlanta Department of Transportation.

Alexander did not respond to requests for comment on Tuesday.

What’s next:

Mitchell, the former city contractor who is the common link to the wider alleged conspiracy, took the stand on Wednesday. He was expected to be peppered by the defense about his work as an informant for the FBI and past legal issues.

The government has yet to outline parts of the alleged bribery scheme that involve contracting in Jackson, Mississippi.