What is luminol and its role in the investigation at Anne Guthrie’s house?

On Saturday, February 7, officers arrived at the home Annie Guthrie and Tommaso Cioniwhere they collected evidence and took some pictures, media at the scene said. The MPs spent about three hours at the house, arriving after sunset and leaving before midnight. Within a short time, X was lit up with people talking about it LaunolA chemical reagent used in forensics to detect trace amounts of organic substances.

parade A conversation with a former FBI special agent Briana FoxProfessor in the Department of Criminology at the University of South Florida (USF) and co-director of the Center for Justice and Research and Policy at USF, explains what luminol is and why it may have been used in Anne and Tommaso’s home.

For starters, Fox tells me that luminol isn’t introduced by “flash.”

“It’s a fluorescent blue light. You need to use it in total darkness,” Fox began. “Basically, the way it works is you shine it and it iridizes when it comes in contact with an organic substance, be it blood, urine, saliva.”

Although Fox doesn’t know for sure if luminol was used in Anne’s home, she says that using luminol is pretty standard protocol.

“There are a couple of things. One is — and I’ve only seen that kind of brief coverage of Annie’s house, and I’ve seen photographs taken — the number one thing you learn at the academy is that you only have a chance to see the road. [a crime scene] once upon a time … The FBI does not do the minimum. They do…everything. There is no shortage of resources. There is no shortage of manpower and time. They go to everyone in every case, every time. And so, if there’s a choice, like, well, can it be relevant? Should we photograph it? No, the answer is you photograph it. I mean, everyone,” Fox continues.

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If the authorities used luminol in Annie’s house, without context, it wouldn’t have set off alarm bells for Fox.

“I don’t think there’s any deeper meaning except that they want to document everything. You never know what’s important. You don’t have the chance to go back at a later date,” she says.

When it comes to why the authorities showed up at Annie’s house at night, Fox believes it was simply a case of “emergency.” Since Annie’s house is reportedly one of the last places Nancy was before she disappeared, it makes sense to do a thorough search. Fox explains that authorities may be looking for anything that may have been left behind… maybe some files, envelopes, pieces of mail, or anything else of that nature that could possibly contain information that could help the case.

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The same applies to vehicles taken for evidence. On Friday, February 6, Nancy’s car was towed from her home.

“They might be searching it for hair or fibers,” Fox says, adding that things found in people’s cars can help authorities piece together clues. “You won’t know until you get that car in, will you?”

Even if the car is not suspected as part of the case, there may never be an opportunity to find it in its current state, which could lead to a “question mark” down the road,” adds Fox.

“How do you know there wasn’t a criminal in the car? So, by crossing every T and dotting every I, they can get potential evidence at that location and eliminate any reasonable doubt that might arise later in the future,” she says.

Read Parade’s interview with Fox here.

This story was originally published by Parade on February 9, 2026, where it first appeared in the News section. Add Parade as a preferred resource by clicking here.