A man like Drew Peterson would tell (threaten) Stacy with, "I could kill you and your body would never be found." I really think that Drew had many scenarios planned out along with places. Drew is not worried about Stacy's body being found. Unless Cassandra messed up his plans, she won't be found. I think that the only hope is that he rushed and was not able to clean up all of the forensics. However, I suspect that he strangled her (got her in a chokehold).
Drew thinks all of this is fun. He thinks that he is smarter than everyone else. I really feel sorry for his kids, especially the two older ones.
I think this is exactly what happened..........he got her in a choke hold and strangled her - quickly, before there were any sounds of a struggle.
DP was sloppy...........he hadn't intended on killing her that day and he had to think as he went along, and he left a lot of clues to his crime.
Like Delta Dawn and Vegas Bride suggested, I also feel that Stacy and DP argued that morning and she confronted him with an ultimatum. He learned that she had an appointment with Kathleen's attorney the next morning and that sent DP into a murderous rage. He feared she would divulge what she knew of him murdering Kathleen.
Like SeriouslySearching said, DP thought everyone would believe him - that Stacy had run off with another man. After all, he got away with Kathleen's murder and the "other man" story had worked for Craig Stebic. DP had friends that would help cover for him too, so he thought he could get away with it. If the news had stayed local, he might have been able to once again, get away with it. Of course, he didn't know then what lay ahead of him, with the national news media and re-examination of Kathleen's death.
And like CuriousityCat said, more often than not these murders happen in sudden rage, rather than being carefully planned.
The one thing that really worries me is DP's apparent confidence that Stacy won't be found. He's way too glib and self-assured.
On the other hand, he had to deal with an unplanned murder and make snap decisions, and I'm hoping he made a mistake with disposing of Stacy's body. I think she is in water - the missing diving weights from DP's garage are a big clue. I think he used these to weigh the container/body down. One of the pings from DP's cell phone places him near one of the canals, and that's another clue. But, he could have been meeting someone in that location too, and I do think DP had some help with the disposal of Stacy's body.
The one thing that makes me feel that this case will be resolved, is the statements we've heard from the ISP. They appear to be confident that the case will be resolved and an arrest made. I'm hoping they do have evidence of foul play and that will result in DP being indicted.
One additional thought about the ISP statement that Stacy didn't leave her home willingly, and that they have evidence. The missing nightstand.........although I believe, like so many here do, that DP got Stacy in a choke hold and strangled her, there could have been a brief struggle and in her attempt to break away from DP, she could have hit her head on the corner of the nightstand. DP could have strangled her on the bed. We all know that head wounds bleed a lot, and there could have been blood on the bed, bed frame, corner of the mattress, something that DP missed when he cleaned up.