How Does a Crime Scene Change?

There is a ton of collet's blood in the master bedroom, but her blood is also in Kristen's bed and one of the girls has brain matter at the entrance of her parents bedroom. So how would all of this happen? There's no blood anywhere else with the exception of Jeffrey McDonald's blood. A lot of the blood that's on the floor is what came out of her as she laid there over time. It wasn't necessarily there at the time the offender or offenders are walking around her body.