Is this a newly installed window? I see the paper still stuck to it.

Would need better pics on the outside.

If this is recent I would assume you have contacted the installation company?

Bingo to the above comment.

Leaking at the window header (i.e. top) and coming through the casing...is 99% of the time a wall or roof issue. Let's see some exterior pics.

Hey guys...so this window is 15 years old...problem is relatively recent. It's the bottom floor(floor level). Only happens during heavy raining

I agree with above. Its time to call the installer and have him come and check it out, and find out where its leaking and get it repaired. If you leave it, you will just have more damage to deal with.

The installer is long gone. Something has obviously failed in or near this window since there are 3 other windows in that room that don't have any issues.

I called a window guy and maybe he sucked at his job, but he looked from the outside and didn't see anything wrong.

The window is not flush with the wall outside, but none of the windows are.

I would find a reputable window guy and call him to come look at it. Something has failed for water to be coming in.

Caulk is not mechanical flashing. Occasional leaks can do serious damage over time. Get someone to investigate immediately.

The framing is dry to the touch. Felt wetness in the middle(at top of window). Could there be a hole at the top of the window that I can't see or feel?

Hello, I found this problem once, the widow leaked, and the leak originated from the roof. You might want to check it out.

Good Luck Woodbutcher

^^^^, exactly, water finds its own way. The leak could be be 10' away. "Most often" it is from a lack of flashing detail but there are no guarantees. And like Joseph said, caulk is a last line of defense and not designed to be the primary waterproofing.

No flashing tape above the window, the tubes appears to be creating a water channel into the house, and why can you pull the siding away so easily?

Tubes = tyvek

Just google window flashing and watch tech techniques. From what i can see in your pics , this was destined to leak .

As Todd said above...it was going to leak. Not a question of how, but when. Nothing is correct about that installation.