The evidence against Kouri Richins is powerful - yet she wasn't arrested for 15 months

I'm going over the various pretrial hearings including the August hearing during which the proecution line up their evidence against Kouri Richins

Their evidence is overwhelming imo.

And yet KR was not arrested for 15 months.

Did police take that long to gather evidence -- or did they simply not suspect her for the first few months and then later began suspecting her?

I know that Eric's family insisted on day one that he has been murdered.

Does anyone know why this investigation took so long?

Were the police taken in by her grieving widow act? Were they bad investigators? Or was it just a tough case for them to prove?

Why was KR walking around free for more than a year?