Based on true events, "Nitram" lives with his parents in suburban Australia in the mid-90s. He lives a life of isolation and frustration at never fitting in. As his anger grows, he begins a slow descent into a nightmare that culminates in the most heinous of acts.
No dogs die. Martin appears to feed and care for the dogs up until he drops them off / abandons them in the middle of a suburban neighbourhood where they run off barking before he drives away to commit his spree.
The man Nitram is based off of (Martin Bryant) is on the spectrum. I don't believe he's portrayed offensively, nor does the film try to imply that his neurodivergent behaviors are to be used as an indicator of potential violent intent.
In a very, very, very vague sense. "Nitram" is the real perpetrator's name, Martin, spelled backwards. The filmmakers fabricate a detail that Nitram is a rude nickname that he was given by bullies in school. There's a scene where he's taunted by someone through repeatedly using the nickname. He, of course, is upset about this.
There's a close bond between an older woman and a young adult man, but it's never described or portrayed as anything other than a friendship. There's one moment of platonic intimacy that can be misinterpreted as flirtatious but, in my opinion, that's only because it's between a man and a woman.
Nitram has an anxiety attack after telling his parents he doesn’t want to live with them anymore, and another very severe one after waking up in the hospital and learning Helen is dead