4th or 5th amendment cases that can have a witness thrown out?

I'm doing a mock trial for Scott Peterson in cl and I want to have Shawn Sibley thrown out, because she only proves that Scott knew Amber Frey, but she cannot prove that he murdered his wife. Are there any 4th or 5th amendment cases that i could present to prove that she should be thrown out? (i've been searching google for hours and I can't find anything)