Wow...I'm impressed. I know several have been sceptical about the Thallium being detected. So am I the little device would have to be pretty sensitive, but I don't have an alternative explanation.
It isn't altogether unlikely. Thallium is pretty nasty stuff and does accumulate in body tissue. Several interesting murder cases have incorporated it - unless you know to look for heavy metal contamination it's a pretty sneaky way to kill somebody. A guy named Graham Young got away with it in the 70s until he started to brag about it.