if he took the bolt out when he wasnt using it he must of been rather concerned about someone else using it.
now was this concern paranoid or was it justified.
Even before the 1989 law that created a statutory obligation to prevent others from using your weapon, there was still civil liability. If you didn't do enough to keep your weapon from being used by others you could have to pay monetary damages for injuries caused.
So the responsible thing to do if you do leave a weapon somewhere else is to do what he did in tkaing the bolt away or use a trigger lock. Of course he could have been lying about taking the bolt to try to conceal he was careless but if that were the case why mention it at all? He could simply have mentioned his shotguns staying and claimed he always took the rifle home no matter what.
A bolt action rifle would have been a crappy weapon to pick for the task of assassinating the family though. You have to have a lot of practice to be able to rapidly fire accurately. Especially if firing from a close distance it can be trouble. While working the bolt someone can charge you and grab the weapon A semi-auto is much better because it fires faster.
A bolt action is better for long range sniper use but not by that much, there are some fine long range semi-auto sniper rifles. A sniper doesn't care about speed of fire though accuracy matters.
BRNO's are inexpensive that is their main appeal. They operate ok for the pricepoint.