Which is why, according to the Fox News article that the FBI asked the parents to pick up some personal items belonging to their son and give the items to them. That way the FBI is absolutely certain that nobody else touched the items other than Brian. There is absolutely no way that the DNA from the parents would get on the items that they picked up and carried across the house to the waiting FBI agents.
Nor is it even remotely possible that the items the parent or parents picked up had ever been touched by anybody else. Like the cleaning person, one of Brian's friends, or even his girlfriend who also reportedly used to live in the house.
What is your point? We don’t know what they took. I suspect some would be grooming items that only he used.