tzatza > Extensive resources were deployed precisely because these normal investigative shortcuts (community tips, suspicious person reports, motive theories from witnesses) were unavailable due to religious prohibition of pointing the finger at someone without proof.
I would think that assisting police is not precluded by laws of lashon hara. American police does not have to follow beis din evidence rules, and modern ability to collect and fuse evidence from multiple sources is something that gemora did not look at. I heard from a rav that he was called to testify against some other yidden and he asked for a psak and was told to fully answer police questions.