Emphasis on subject like english language

Emphasis on subject like english language
 

Could you help me how can i emphasize on subject in spanish? For clearfying please translate these sentences to english:

I washed myself in bathroom.

I am the one who washed him in bathroom.

I am the one who washed myself in bathroom.

For better understanding examples in a dialog:

-Mario told me that your father washed Smith yesterday. Is it the truth?
-No, I (not another one) washed him in bathroom.

-Mario told me that your father washed you yesterday. Is it the truth?
-No, I (not another one) washed myself in bathroom.

Can "A si mismo" be used for this purpose?

soy yo quien ... (did this, do that, will do it)
soy yo el/la que ... (did this ...)
somos nosotros quienes...
son ellos quienes...
somos nosotros los que...
somos nosotras las que...
son ellos los que...
son ellas las que....

So yo el que respondió tu pregunta.

Thanks, are these forms common in Spanish? For example assume another dialog:

Teacher: i've doubt that you do your homework? Did another person do that?

Student: Be sure. I, not another one, did my homework.

In a common spanish, do we sound this translation:

Asegúrese. soy yo el que hizo los deberes.

No lo dude. Fui yo el que hizo los deberes.

(You may use also "soy" as you were and continue to be yourself, but it's who did it the matter)