Just saw a doc on the Tracy Andrews case.
She hid the murder weapon/knife in her shoe.
She managed to dispose of the knife later, probably in hospital. But kept the shoes.
Later investigations found blood in the shoe inprinted in the shape of a knife.
The police were struggling without a murder weapon but now had a narrative.
Similar to the silencer, the shoes should have been cleaned or disposed.
In hindsight a mistake but these people are not criminal masterminds.