Fires, Basements, Kind strangers, and the fire dept.

So my house almost caught fire today.
Not too long ago actually.
Still kind of shaky.
The fire was located in the window well.
But the fire dept. said that the fire was started in our basement and moved to the window well.

We had no idea it was on fire
but some kind stranger came running up to the front door and said that there was a fire
My mom brother and I went out to the front yard and the guy showed us over the fence the black smoke coming up from the window well.
My mom ran into the house immediately to call the fire dept.
I ran straight to the backyard and looked down the window well and saw the fire.
I quickly turned the hose on and grabbed it and pointed it down into the window well to put out the fire.
Once the fire did stop I ran into the house to tell my mom that I put it out.
She told the fire dept that I put it out.
They told her to get everyone out of the house and they were on their way.
They got here fast cause we barely walked out the front door and they were here.

There were 4 of them.
Two went down into the basement with my dad at first and another two were out by the window well.
The guys in the basement opened the window to the window well and investigated huge chunks of burned plastic.
They opened the window well and removed the huge chunks of plastic and found nothing that could have started the fire.

They left the window but did not leave the basement and the two guys that were outside stood in the front yard and waited.
Like 3 minutes later my dad comes out and tells my mom to go inside.
She was inside for like 5 minutes or so then calls Ray in.
That was when they discovered that the fire started in the basement before it made its way to the window well.
And since my brother was the only person to be in the basement at all today he was prime suspect.

I think he did it.
It is pretty obvious cause no one else was in the basement today.
But the fire guy aparently questioned Ray and Ray said he didn't do it.
Ray came outside.
And like 5 minutes later they left.

We are all safe.
The house is fine.
The basement is fine.
It just smells like burnt plastic.

Nothing was damaged.

But we still don't know how it started.
I hope we figure out how it started.
It was really scary.