▁costs ▁in ▁long ▁and ▁complex ▁cases . ▁Intel lect ual ▁property ▁and ▁medical ▁neg lig ence ▁cases ▁are ▁typical ▁examples . ▁ ▁Electron ic ▁evidence ▁has ▁also ▁entered ▁the ▁court room ▁as ▁critical ▁for ens ic ▁evidence . ▁Audio ▁and ▁video ▁evidence ▁must ▁be ▁authentic ated ▁by ▁both ▁parties ▁in ▁any ▁lit ig ation ▁by ▁a ▁for ens ic ▁expert ▁who ▁is ▁also ▁an ▁expert ▁witness ▁who ▁ass ists ▁the ▁court ▁in ▁understanding ▁details ▁about ▁that ▁electronic ▁evidence . ▁ ▁Vo ice - mail ▁record ings ▁and ▁closed - circ uit ▁television ▁systems ▁produce ▁electronic ▁evidence ▁often ▁used ▁in ▁lit ig ation , ▁more ▁so ▁today ▁than ▁in ▁the ▁past . ▁Video ▁record ings ▁of ▁bank ▁rob ber ies ▁and ▁audio ▁record ings ▁of ▁life ▁thre ats ▁are ▁presented ▁in ▁court ▁rooms ▁by ▁electronic ▁expert ▁witness es . ▁ ▁R ules ▁of ▁evidence ▁and ▁code ▁of ▁procedure ▁ ▁H ears ay ▁rule ▁ ▁One ▁important ▁rule ▁that ▁applies ▁to ▁the ▁expert ▁witness ▁but ▁not ▁the ▁per cip ient ▁witness ▁is ▁the ▁exception ▁to ▁the ▁he ars ay ▁rule . ▁A ▁per cip ient ▁witness ▁tells ▁only ▁what ▁he / she ▁actually ▁knows ▁about ▁a ▁case ▁and ▁nothing ▁more . ▁Per cip ient ▁witness es ▁cannot ▁give ▁opinions ▁nor ▁conject ure ▁regarding ▁a ▁hypoth et ical ▁set ▁of ▁conditions . ▁Con vers ely , ▁the ▁court ▁does ▁allow ▁an ▁expert ▁to ▁test ify ▁about ▁issues ▁that ▁may ▁not ▁be ▁personally ▁known ▁by ▁them . ▁This ▁allows ▁the ▁expert ▁to ▁rely ▁upon ▁scientific ▁articles ,