David has even said the police found a silencer on the day of the massacre.
The police had Sheila's blood which they could insert. They could scratch the aga & dispose of specific photo's of the aga. Then send the silencer away for testing.
It was a big frame, in a big case. Jobs, pensions, reputations & criminal charges were at stake.
Why risk making it 10x harder by involving law abiding citizens when they didn't need to ?