These are the sorts of seemingly benign mistakes that can haunt you in court, and time of death is especially tricky. It’s not an exact science but is crucial to any alibi. It’s a favorite bone for defense attorneys to chew on, and how quickly strangers can lose faith in what an expert witness like me testifies. I have no intention of causing jurors to doubt my credibility because an inexperienced detective thought he could do my job for me at a death scene.

While it was appropriate for Barclay to check that the victim was actually deceased, he shouldn’t have begun playing the role of a medical examiner by making determinations about rigor mortis and how advanced it is or isn’t. He needs to be careful about information he finds on the Internet. He shouldn’t accept as gospel what the temperature in Cambridge is based on a weather app.

What part of Cambridge? There could be quite a difference between a shady spot near the water and the hot bricks of Harvard Square, for example.

“I’m assuming you got the temperature from some sort of app on your phone,” I say to Barclay after a silence I can tell he’s eager to fill. “So the detail about it being eighty-eight degrees Fahrenheit or thirty-one degrees Celsius? We’ll keep that out of any reports since we don’t know what the temperature is in the exact location where the body was found.”

“If you got a thermometer I can put it over there next to her,” he says, and I realize how aggressive he is.

“No thanks. That’s not what I was suggesting. I don’t have my scene case yet, but when I do I’ll handle any temperatures that need to be taken of the body, the ambient air, and all the rest.” I speak slowly and in a measured tone, resorting to what I think of as my neutral voice. “It might be cooler here because of the river,” I suggest as if it’s no big deal.

But he knows it is. He feels disrespected and criticized, and I’m witness to his mood’s rapid shift. It’s something I suddenly remember observing about him on the few occasions I’ve been in his presence. He’s volatile. He goes from hot to cold with not much in between.

“If only there was a breeze.” He looks away from me, toward the river, and it’s obvious when his narcissism is winged. “It’s hard to breathe. Damn suffocating.”

He’s practically turned his back to me.

“WHAT TIME WAS THE body found?” I ask him that next, and he can keep his back to me the rest of the night if it makes him happy.

After a sulky silence Barclay says, “We got the call about forty-five minutes ago. But oh! Wait a minute!”