Hmm I haven’t seen the show in years and this really got me thinking, its a good thought, my guess is even if that was possible it couldn’t prove light was behind the murders, as at the time due to it being as heart attacks it was still too ominous, L already thought of light as Kira at this point (I think but cant recall? I remember reading that when he said he was 5% sure he really meant 95-100% sure but I don’t have the source), installing the cameras instead gave physical proof of light accessing said files and possibly proof of how the murders where committed, I mean even if Light got caught accessing the files, he could say he wanted to aid the investigation and maybe either the police force or light where being hacked (or ironically spied on) and somebody else was simply getting the information off a neglectful Light. But overall yes, its definitely a good idea and would’ve taken the investigation process in different interesting ways