As more witnesses testified Monday about threats and intimidation by DeKalb County CEO Burrell Ellis, his assistant tried to avoid speaking against him in court, invoking her Fifth Amendment right not to incriminate herself 30 times.

The judge presiding over Ellis’ corruption trial ordered the assistant, Nina Hall, to answer questions in all but a few cases.

Hall was one of several government employees who took the stand Monday in the case against Ellis, who has pleaded not guilty to charges that he strong-armed contractors into giving contributions during his 2012 re-election campaign. Ellis, who as CEO ran the day-to-day operations of Georgia’s third-largest county, is at the center of the biggest corruption trial in metro Atlanta since former Atlanta Mayor Bill Campbell was convicted in 2006.

Hall told jurors she overheard a heated phone conversation between Ellis and Joanne Wise, who worked for a technology contractor called Ciber Inc. and refused Ellis’ pleas for a donation in February and March 2012.

“He was angry they had not returned his phone call, that there was no excuse for them not having returned his phone call,” Hall said after Superior Court Judge Courtney Johnson ordered her to answer questions. “He indicated he was going to tell their boss they provided poor customer service and they were rude.”

With her attorney sitting by her side at the witness stand, Hall wouldn’t respond to questions about whether she had taken money from vendors or had perjured herself in previous testimony to a special grand jury. District Attorney Robert James had told Hall’s attorney on a recorded phone call played in court last week that he didn’t plan to prosecute her.

Hall’s words backed up Wise’s statements from earlier in the day, when she said Ellis repeatedly haggled her for contributions even though her company had a policy against making political donations.

Wise said Ellis mixed his job as the leader of DeKalb County’s government with his re-election campaign. In phone calls to Wise, Ellis introduced himself as the county CEO and talked about how she and her company had benefited from doing business with DeKalb, she said.

“He was irritated and annoyed that I was not calling him back,” Wise said. “He said, ‘You will not get any more business from DeKalb County, I can tell you that.’”

Ellis’ defense attorneys have argued that he was upset with companies that disrespected him by not returning his calls, and whether they gave campaign contributions wasn’t important to him.

But prosecutors have pointed out through witnesses that Ellis was never calling about county business — he was always asking for election money.

Wise told Ellis that her company wasn’t going to do business with DeKalb anyway because of a disagreement over contract terms.

“He said, ‘That’s a good thing, because you weren’t going to get more business anyway,’” Wise said in court. “And then he said, ‘and you call yourself a good mom.’”

When a different company, National Property Institute, also declined to contribute to Ellis’ campaign later in the year, he asked a government employee to arrange a meeting.

The employee, DeKalb Community Development Director Chris Morris, said Ellis wanted to discuss the company’s lack of responsiveness to his phone calls.

Morris said she didn't believe Ellis when he told her the October 2012 meeting wasn't about political contributions.

“My impression of what the meeting was about, really, was that the meeting was about a campaign contribution,” said Morris, who has worked for DeKalb County for 38 years.

After the meeting, NPI gave Ellis $2,500 and didn’t lose its $1 million contract with the county to rehab foreclosed homes.

In all, Ellis raised $1.5 million for his campaign and easily won re-election.

But six months into his second term, in June 2013, a grand jury indicted Ellis, and he was then suspended from office.

Ellis faces 13 criminal charges including bribery, extortion, theft and perjury, and he could face up to 20 years in prison if convicted on the most serious count.

As soon as Tuesday, Jurors could hear secretly recordings of discussions between Ellis and a cooperating witness for the prosecution, former DeKalb Purchasing Director Kelvin Walton.

Once the prosecution finishes presenting its case, Ellis’ defense team will have its chance to attempt to clear his name.