Tomasi is charged with one count each of murder and attempted murder.
Prosecutors say Tomasi used a knife in a domestic violence incident January 8.
They say he allegedly stabbed his live-in girlfriend, and then proceeded to fatally stab one of her children.
The defendant is not the biological father of the child victim.
Authorities said the couple has a blended family and lived in the home with eight children.
Tomasi was ordered held on $2 million bail. He faces life in prison if convicted as charged.
