If the only info they had given was that his father was abusive - it potentially could be a motive if the person who he had allegedly murdered was his father, or someone he knew did something similar in a way to get revenge for his mother.
However! While it is a traumatic event and likely could (and would) have emotionally and mentally scarred them, it’s also possible that they could be extremely sensitive to violence because of it - making them the opposite of a suspect, as they physically wouldn’t be able to cope with the sight again because it would bring back all those memories.
Unless they directly confessed to the murder, or let something slip that connects them to the crime scene or the situation - it’s also equally possible that they’re innocent, but that the event does just bring back the memories from his childhood trauma.
Just another perspective from someone who is way too obsessed with True Crime documentaries! Hahaha :p - Also moving this thread to “Off-Topic Discussion”