PH comes across as an innocent, old man in the channel 5 documentary. He may well be innocent, but I still find it telling that he lied about his whereabouts when first questioned.
Ann also seems to be a somewhat strange character. She leaves her 5 year old son and moves in with PH. On the day she's murdered, she's mid 40s, yet going to an 18th birthday party. Two witnesses (one who knows her) see her driving people about in the afternoon.
It could be argued that PH does everything possible to place himself away from the crime scene. After the murder, he's insisting that Ann didn't sunbathe in front of passers by, yet Ann's friend SE saw her sunbathing that afternoon as she drove past. The Ch5 documentary also shows several photos of Ann sunbathing outside.