Newsround's Lizo Mzimba went to America to find out more about the US sniper.
Thanks for all the questions you sent in for him!
We put some of them to him, and here are his answers.
Are the FBI sure that John Allen Muhammad is the sniper?
They seem to be. It looks like the evidence they have is enough to take the two people they have in custody to trial.
Is the sniper part of the al-Qaeda network?
If these men are the snipers, no one yet knows why they did it. So far, no one has linked them to al-Qaeda.
What proves that the same person killed all those people?
There is no confirmed proof yet, and that will need to wait for the trial. But the police evidence indicates that the same weapon was used in all the shootings.
Now they've been caught, what will happen to the two men under arrest?
It'll be decided if and where they'll go on trial. That could take weeks - and because the police need to get all their evidence together, it might be months or even years before the trial actually takes place.
How many police were involved in the hunt for the sniper?
Hundreds of police from several different areas covered a huge area of land in the search for the sniper.
Why was it so difficult for the police to find the sniper?
One reason was because the attacks were very random, shooting different types of people in different places at different times of the day. That made it very difficult to work out where they might strike next.
How has this affected the children and residents in Washington DC?
People have been affected, frightened to go out, and lots of outdoor events were cancelled. But now two suspects have been arrested, things are getting back to normal.
Were you scared out there?
Not really, I don't really think about it.
Are children safe, or might there be another sniper in the future?
These types of attack are very, very rare so it's not something people should worry especially.
Is it important that one of the victims was an FBI employee?
It might help decide how and where the trial might be held, but there are very complicated discussions going on to decide what will happen next.
Could something like this happen in the UK?
These type of attacks are very unusual in America, where it's much easier for people to buy guns. They're even harder to get in the UK, so I wouldn't worry about it happening in Britain.