Unfortunatley, I think if police had gone to the door to do a welfare check, they would have found nobody home, everything to be just fine/no sign of trouble and left. They would not have busted down the door. I think it's unlikely that DW would have answered or permitted one of the other hostages to answer the door. The only thing I can think of that might have changed the outcome is that if couple patrol officers knocked on the door, DW might have decided to screw the whole thing and highed tail it out of there ASAP after LE left, without setting the fire for fear of drawing attention back to the house.
The horror is that Mr. S might well have been ordered to go to the door and just as he had done via the phone, he would have made LE think all was well. One of the reasons I envisage more than one holding the four is that Mr. S was monitored on the phone so that anytime he might have alerted anyone, an accomplice could threaten or actually harm PS.
JMO one person monitors Mr. S at all times (and certainly if he was ever out of restraints) while one, in sight of Mr. S., demonstrates his capacity to harm PS at all times.
Mr. S. probably had a strong ability to weight benefits and risks, as well as an instinct about people, and in particular, any adversary. We know, based on the public record now, that DW was unhinged, impulsive, rage-driven, sociopathic, and impervious to consequences. Despite all his brushes with the law, and risking deportation, he continued to threaten, terrorize, stab.
JMO Mr. S. saw that DW would not hesitate to go for broke as LE closed in. DW had warned Mr. S.,and moreover, he had demonstrated on PS that he meant business and would not be deterred.
Mr. S. could not take a gamble. Had a knock on the door come from LE, either he would have assured them by phone or at the door, knowing that any tip-off and DW would "cut his losses," just as Komisarjevsky and Hayes did in the Petit case. DW's last last Feck you to the world would be to kill PS. Mr. S. had made an assessment and continued to as the hours went on.
What we are asking is 1) any way this horror could have been prevented? 2) any way it could have been stopped once underway?
It's the what ifs that will continue to haunt survivors. The rest of us would like to think in the same situation we could control our fate and the fate of those we love. This case forces us to think twice.
JMO Once inside the house, all bets were off. Mr. S., his family, Mrs. F. I am sure did all in their power to survive. Once inside the house, a monster and possible accomplices were in control. They gained control of PS and thus from then on, Mr. S. could only buy time, try to offer them something to make them go away, comply with their demands.
The one solace for the public (what solace can there be but a higher power for survivors?) is that DW must finally face justice and comply with it. He can never be in control again. Justice may come too late, but it will come. It has come for him.