Is there a single word to lay emphasis on something?

Is there such a word that does this?

He's a scientist, a natural scientist _______.
That is a crime, a federal one _______.

A single word which emphasizes a preceding statement by/and giving additional information, used more often after the phrase being emphasized, and not exactly "not to mention".

He's a scientist, a natural scientist to boot.
That is a crime, a federal one at that.

And if you absolutely insist on it being a single word, you can use even or actually.

I'll add in my 2 cents for no less, as in:

He's a scientist; a natural scientist no less.

You can try specifically:

From Collins Thesaurus of the English Language:

adverb
2. precisely, exactly, explicitly, unambiguously - brain cells, or more specifically, neurons

Therefore:

He is a scientist, a natural scientist specifically.

That is a crime, a federal crime specifically.

You can also put it in front of the additional information:

That is a crime- specifically, a federal crime.

^{_{1. Collins Thesaurus of the English Language – Complete and Unabridged 2nd Edition. 2002 © HarperCollins Publishers 1995, 2002}}

You could consider using indeed which is an adverb:

Used to emphasize a statement or response confirming something already suggested

Used to emphasize a description: 'it was a very good buy indeed'

Your example:

He's a scientist, a natural scientist indeed.
That is a crime, a federal one indeed.

[Oxford Online Dictionary]

Consider "as a matter of fact":

He's a scientist, as a matter of fact, a natural scientist.

That is a crime, and as a matter of fact, a federal one.