Regarding Ashland (it's MA, BTW), I found this: Ashland Teen Faces Decade in Prison for Defacing Hindu Temple
On November 27, 2003 Metro West reported that "an Ashland teen faces more than a decade in jail if he is convicted of spray painting hate messages on a Hindu temple in Ashland on Halloween. Anthony Picciolo, 17, of 15 Roberts Road was released without bail by Judge Paul Healy at his arraignment yesterday in Framingham District Court.I hope he got all 10. I am not optimistic. I can't find an update on this. None of the advocacy sites ever talk about sentencing.
About the Matawan incident, I can find that "Vandals threw a Molotov cocktail at a Hindu temple in Matawan" shortly after 9/11. "Firebombed" might not be strictly correct as it is not clear that the attack actually caused any fire. It may have been lit, I don't know.
In fact, other than lists of reported post-9/11 hate crimes, I can find no details other than that sentence. (Well, some reports used "firebombed" but no other details.) I was hoping to find something on whether anyone was charged, you would think it would have made some of the papers and some details would have found their way to the net.