Grimmauld had been a challenge when the Order had used it as a headquarters and again after Snape had defected and exposed its secrets. Charlie had only been in it in passing since Harry had reclaimed it: one of his many regrets about his dead friend. There were a lot of should-haves and would-haves about Harry. Finding his killer wasn't going to be one of them.
He'd approached the house from the alley behind and spent the time to work his way through the wards quietly, just as he and Bas had done at Dudley's apartment--poor dead Dudley, who'd been in the wrong place at the wrong time--and enter from the rear. He'd carefully explored the kitchen (trashed, but warded as a crime scene) and the back of the house before moving quietly forward to the front.
There was a bloke sitting on a suitcase in the parlor.
Charlie pointed his wand at the apparently-oblivious fellow and stepped into view. "Who in Merlin's name are you and what are you doing here?"