(at around 33 mins) Tom Barnaby is looking at crime scene photos of the body of Frances Trevelyan. There are two photos of her out stretched hand and the phone on the floor. In one photo her hand is noticeably closer to the phone than in the other.
Barnaby and Jones enter Mrs. Beverley's home , awakening her during the night. She calls out and tells them to come through to the bedroom. The moon is the only source of light, so she reaches over to turn on the bedside lamp. When they enter her bedroom, the lamp on the table near the door is now on too, although she hasn't gotten out of bed to turn it on.
There is much discussion about fingerprints on the pot that killed the victim and whether the accused wore gloves. On the stand, Barnaby testifies that the fingerprints could not have been wiped off because previous users' prints were still on there. When the killer is revealed, the flashback has him not wearing gloves and wiping the pot and the cell phone of prints.