Q: Are the Jews who were killed in the terrorist attack in Pittsburgh considered holy? Does it make a difference that they were in a non-Orthodox synagogue?

A: They are certainly holy and they died sanctifying Hashem's Name. There are 4 levels of a Jew being called "Holy":

1. The Chatam Sofer #333, based on Sahedrin 47, says that if a Jew is killed by a non-Jew in a robbery he is called "Holy". See Rashi on Tehillin 79:2.

2. In Shut Maharil #99, based on Semachot 2:11, it says that if a Jew is killed because he is a Jew, all of his transgressions are forgiven, he died sanctifying Hashem's Name and he is supremely holy. This is what those murdered in the Holocaust are called. See also Rambam, Hilchot Yesodei Ha-Torah 5:4. Rama, Yoreh Deah 340:5. Taz, ibid.

3. At a higher level is one who is killed because he refuses to worship idols, as explained in Rambam, Hilchot Yesodei Ha-Torah Chapter 5.

4. And on the highest level is a soldier who risks his life to save Jews. No one can compare to him. Pesachim 50a.

The first two categories apply to one who is killed in a terrorist attack, and the fourth category perhaps applies to a terror victim who lives in Eretz Yisrael (as every Jew living in Eretz Yisrael is considered a "soldier").