I think in this case detective work rather than forensic work is going to be more useful in finding out whether the items belonged to him. After all this time, I think it would be difficult to prove this. However, if these had come from a modern crime scene, there is actually something we can do with them. Hats are especially good because we can usually extract DNA from headbands. However, in this person's case, they'd be better off popping it along to the Essex Police museum and seeing if they can match up the item from the period with the photograph. Cross contamination is also a major problem for us when using DNA. DNA is great and helps us out a lot, but it also presents its own problems.

Well it's actually extremely difficult. Cross contamination is a big problem, and so first of all you have to make sure that your sample is clean. If the person excavating it touched it, you don't want to end up extracting their DNA by accident. We bleach it to get rid of all the DNA on the outside and then have to try and find some cells inside the sample that are still whole. We then break those open and extract the DNA.

There is a national DNA database. When offenders are brought in, we take a sample of their DNA and it goes onto this database. Later, we try and match stains from a crime scene to people on that database. Obviously this assumes that the DNA is already on the database. This means that unless we have a suspect, there'll be no match.

On the 27th edition of the Naked Scientists, John from Clacton said he saw a bright flash in the sky, and wondered if it was a gamma ray burst. Our guest on the show, Mike Hobson, said it definitely couldn't be a gamma ray burst because our eyes aren't sensitive to gamma rays. However, without having seen it, he wasn't sure what it could have been. Matthew says that there are a network of satellites used for a satellite telephone system called Iridium. They're in a low Earth orbit and have large solar panels that can catch sun light and reflect it down to the Earth. They appear as a bright flash that lasts several seconds. This is a potential explanation for what John saw that night.

It's pretty difficult to say exactly where we came from, but the evidence is stacking up that we came from Africa, probably about 100 000 years ago. This is based on a combination of looking at the Y-chromosome in DNA, which is the male line, and also mitochondrial DNA, which you have to inherit from your mother. There's a lot more diversity in Africa than anywhere else, and it looks like we can track the migration of humans around the world. East Africa is looking pretty good as our origin.

With the number of strands we actually look at, it means that the chances of it being someone else are about one in a billion. The biggest problem that you have with DNA as opposed to something like a fingerprint, is that if your fingerprint is at a crime scene, there's no doubt that you've actually been there. With DNA, you have to eliminate the possibility that it was brought in by someone else and caused cross contamination of the evidence. It is a very real issue for us in investigations, but it something that we are always aware of and try to rule out.

You're right. A bone marrow transplant can cause a problem because what you essentially become is a mixture of two people. Someone takes away your normal bone marrow and replaces it with the bone marrow of somebody else in order to make up for the damage caused by your own bone marrow. This means that you potentially leave behind two DNA fingerprints at a crime scene and could even implicate your donor.

You can definitely get rid of DNA because there are enzymes which the body makes and are found in the environment called DNAase enzymes. This means that they literally eat DNA and cut it up. So you can definitely get rid of DNA. Leaving DNA in the sun can also break it down. Changing DNA is actually very different. Changing happens in all of us due to a process called mutation, in which your DNA accidentally swaps a few of the DNA letters around. These letter swaps usually get fixed by DNA repair machinery within the cell. If it's not, it can sometimes lead to cancer. However, there's not actually a technique in which you can physically change DNA, say, at a crime scene, to implicate somebody. The best way to do that is to literally sprinkle some of their DNA at the scene.