The mistress that prosecutors call the motive for Michele MacNeill's alleged murder testified Friday about her interactions with Martin MacNeill right before his wife's death in April 2007, PEOPLE reported.

Gypsy Willis, 37, a former nursing student, first met MacNeill online in November 2005.

"We would see each other a couple times a month," Willis said.

When asked when the relationship with then-married MacNeill became sexual, she replied, "In January 2006. It was a casual thing, whenever we had time and it could be arranged. I think we'd have sex half the time. Sometimes we'd just have lunch." 

MacNeill has been accused of overmedicating and then drowning his wife, Michele MacNeill, in their home in Pleasant Grove, Utah. He reportedly forced her to get a facelift and requested a plethora of strong medications from the doctor.

Prosecutors say his motive for killing his wife was to be with Willis, who was hired as a nanny in the MacNeill home soon after Michele MacNeill's death to take care of the younger children.

Willis was questioned about the bizarre meeting that she and MacNeille orchestrated so she could meet his children. Just days after the funeral, MacNeill and Willis pretended to meet for the first time outside a Mormon temple. Willis admitted in a police interview that the meeting was staged.

"I was supposed to walk up and introduce myself, and maybe strike up a small conversation," Willis testified. "[MacNeill] wanted me to meet his family on the best possible terms." 

Prosecutors also quizzed Willis on the flurry of texts between her and MacNeill on two significant days: April 11, 2007, the day Michele MacNeill was found dead, and the day of her funeral.

The couple exchanged about 30 texts on the day his wife died. The content of the conversations has not been revealed yet. Rachel MacNeill, one of the couple's eight children, testified Thursday about her reaction to Willis' presence in their home, The Salt Lake Tribune reported..

"I expected her to be focused on the children, to cook or clean or take care of the children," Rachel MacNeill testified. "[Instead], my dad was cooking, she was staring at my dad. There was nobody looking after the children."

MacNeill and Willis were both convicted of identity theft in 2009, according to PEOPLE. Willis, who served a 21-month sentence in federal prison, is testifying as part of her plea deal to avoid further time behind bars. 

Willis resumes testimony Tuesday.

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