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Welcome to CNN STUDENT NEWS.

I'm Carl Azuz.

Today show leads off at the latest developments surrounding Monday's terrorist attack in Boston.

Authorities say, they are making significant progress on the case.

As of yesterday afternoon, no arrests have been made.

Three people were killed and more than 180 others were wounded, at least 100 of those people have been released from local hospitals.

President Obama is scheduled to be in Boston today,

he was planning to attend an interfaith service this morning that's dedicated to victims of Monday's attack.

We now know the identity of all three people who were killed in the bombing.

Yesterday, we talked about Martin Richard and Krystle Campbell.

The third person is Lingzi Lu.

She was a graduate student from China studying math and statistics at Boston University.

Authorities are working through all the evidence including fragments that they think were part of the bombs.

Tom Foreman has more on the investigation efforts and how technology that's used for the marathon could help out.

Investigators seem to be focusing on three critical hours near the finish line:

one hour before the elite runners came sweeping up Boylston Street, they did one final security sweep, checking for bombs there.

Then 17,500 runners or so came up, crossed the finish line, and other 6,000 were on their way when the first bomb went off,

about three hours after that security sweep.

12 seconds after that, the second bomb went off, some distance down the road.

So, what are investigators looking for?

Let me rotate this around so you can look right down the race course here.

They are looking for anybody who saw something in this area that would directly relate to the dropping off of a package,

somebody doing something suspicious that would really jump out.

That's what they are asking for.

All those photographs, all that video to see if they might find clues to things like this:

this photograph has attracted a lot of attention, because you see that package sitting right there?

That's right, near the spot where there was one of the explosions, a lot of people are wondering if that was one of the parcels that may have been dropped off here, that blew up.

So, investigators are going to try to find people who can say, yes, I saw someone with a package like that.

Yes, I saw this person leave it there, that sort of thing.

It's a tricky job to get done,

but they have something that might help them out that's really unique to a race circumstance like this:

every single runner on this course had to wear an electronic tracking tag, that's how race officials keep track of who's coming down the course.

Now, the runners may not be able to tell them anything,

because they were focused on running.

But the runners would know where family and friends had gathered along side, to watch their progress.

So, if investigators say, look,

we have a witness here who says they saw a man with something,

and we have one down here who says, they saw - that they think is the same man, this would allow investigators to go through the runners,

through the race organization and say, where were your family and friends?

Where they in the middle here?

Did they see this person pass by?

Something that they may not think much of it, now, may really matter.

Normally, investigators would have to wait for those people to come forward.

In this case, they have a way to reach out to them, and that could prove very important.