Thai police say the suspect killed his grandparents at home before going on a rampage at his school on the outskirts of Bangkok.
"It's been a devastating few days," Michael Simpson said.
Arday shared his resignation in an open letter on Wednesday.
Christopher Clancy said Lindsay Clancy and her son had "all-American family."
The new specials airing on The History Channel and Lifetime mark the 25th anniversary of the Sept. 11 terrorist attacks with unprecedented access and firsthand accounts.
President Donald Trump's pick for attorney general, his former personal attorney Todd Blanche, appears to be in jeopardy as several key Republican senators raise concerns.
