The military said preliminary reports do not indicate the crash was caused by enemy fire, and the cause is under investigation.
The gunman had been married to the woman he killed, and the man fatally shot is believed to have been dating her, police said.
The arrest follows a tumultuous day when dozens of students walked out of a forum attended by the school's chancellor. The school has been roiled by at least 12 racist and bias-related episodes since Nov. 6.
When Viktor Usov's feline, Sasha, went missing in 2014, he assumed the cat had been eaten by a coyote.
A teen from the Chicago suburb of Naperville posted the classmate's picture on Craigslist with a caption that included a racial slur, police said.