In this case, there are 5 suspects and all are plead innocent. Assuming that only 1 person guilty, then it should be 1 person lying that get negative reading and 4 people telling the truth that get a negative reading. The chance for negative reading is:
when telling lie= 100-95%=6=5%
when telling truth= 100-10%=90%
Then the chance would be: 5%* (90%^4)= 3.2805%