@Skyblueday32 you raise some great questions, perhaps these answers will help...
Let's run with the assumption that it was a murder-suicide and suppose a few thinks intertwined with facts that are known.
Why call the police. I don't think the original plan was to call the police. My theory is that Dick left the package on the front porch intending to "recover" it when he got back from dropping the boys off at school. The boys saw the box and brought it into the house where it was initially left unopened. Pat opened the box and brought the contents to Dick's attention. At that moment in time, the plan started to crumble, in that, if this was a murder-suicide, Dick had to maintain the "shock" value and not alert Pat to the impending doom. Logically, calling the police would make sense, but in doing so, he sent the older boys back out into the car.
Remember, at this moment in time, the boys had less then 30-seconds to actually see the bomb, so the fact their memories and descriptions were so accurate doesn't gel with a quick peek at the device.
Pat's suspicion was now on high alert, Dick had to call the police, because logically if he didn't, she would be on alert, and based on the fact that his plan was for the boys to be gone, he needed someone there (the police) to tend to the boys given what he knew was about to occur.
He goes through the motions, yucks it up with dispatch, and then the moment of no return happens when the officer pulls up to the house. It was DO or DIE time, he was either all in, or about to be caught.
Think about this if a bomb had just been delivered to your door, wouldn't the logical thing be to get out of the house? Even if this was a sick prank, GET OUT OF THE HOUSE, and yet he didn't, they didn't, he didn't want them out, just the boys - and when the cop showed up, he had to detonate. it was the point of no return.
So he triggered the bomb.
Remember, the boys were supposed to be at school, but he went out knowing at least a cop was there to tend to and care for the boys - it was over for him and Pat.
But that circles back to the "WHY" of this case, and that is the item every has always struggled to answer. Why kill Pat and himself?
I think the answer returns to the church.
The church, Middlesex Bible Chapel (MBC), was part of the Plymouth Brethren denomination, a strict and very legalistic church, that while meaning well, could be viewed very negatively by outsiders.
The boys, were, to put it mildly, boys! That means, they weren't always on their best behavior, and yet, at MBC, children were expected to sit in silence, well behaved, and participate in services. They didn't have kids church, or an outlet that afforded kids the opportunity to learn as kids learned - they were expected to sit, to listen, and if Dick & Pat were anything like my own parents (Remember, we (I) attend MBC as well), they were probably quizzed about the sermon on the drive home or over Sunday lunch.
The elder/deacon board had strict rules for serving/leadership roles, and it is my belief that Dick sought those roles and enjoyed the "prestige" leadership brought - however - he was called out and told he would be stripped of his leadership role if he didn't bring his own house into order.
My own father was at that meeting, and has always maintained that Dick felt it was the churches responsibility to raise the kids, and that he'd see to it that that occurred.
Does that justify a murder-suicide, no, and yet, the fact the no suspect has ever been found, no arrest ever made, no death bed confessions proffered by a guilty soul, nothing, nada, zip.
And the church circled the wagons, Dick and Pat went down as saints, I'd argue the rest of the world none the wiser to the events occurring in the weeks/months before the bombing.
I grew up in that church environment, not just at MBC, but multiple Plymouth Brethren assemblies across the country - they are all very similar in their legalistic approach. I, along with my sister attended Green Brook Christian Academy, the middle boy was in my 2nd grade class, our teachers name was Ellen Barnes ( I remember because 7-year old me had a crush on her!).
After the deaths, the boys spent weekends at our house, my parents along with several other families in the church expressed desire to adopt the boys.
I'm sure I'll post more later, but for now am curious as to your thoughts on my thoughts....