Hello, new here. I live about an hour away in Noblesville, IN. My wife grew up right next door to Delphi, so we have been following closely.
In my opinion this is a crime of opportunity, but with pre-mediated intent and planning beforehand. This took place on a Monday, which was recognized as Presidents day by the school systems. The perp knew that the kids were not in school on this day. Not only that, it was unseasonably warm, I remember it being somewhere in the low 60s I believe. Central Indiana had a few days of great weather and I think the perp purposely set out knowing that children were out of school, and would be outside enjoying the warm weather in a usually cold February. I think he also recognized that this trail wouldn't be as busy with adults, because most adults work on Presidents day. He most likely grew up in the area as a kid, or worked in the area and knows it well. Maybe he took Presidents day off himself, and was visiting his sick and elderly mom or dad for a three day weekend.
He walked along the creek during the morning, kind of planning out how he would do the crime in his head and where he would make the victims walk to. He could have watched the girls from a distance, and as they got on the bridge, he followed. He may of casually passed them on the bridge once, to get a closer look at their size and vulnerability. Maybe even walking to the beginning of the trail, to make sure no parents or other people were around. Then heading back directly towards them. This could have been when the girls sensed danger. One girl pulled out her phone and pretended to be taking a picture of the landscape, but recording him the whole time. Maybe at the point when he intercepted them, he either took the phone, or she put it in her pocket. I hope she put it in her pocket, and there is a lot more of the recording to help LE. Hell, they could even have the whole murder on audio. I remember one LE saying this is the most evil thing he has seen in 30 years of law enforcement. I'm guessing he came prepared with a gun, knife, rope, maybe zip ties, etc. Most likely he only hoped to find one lonely woman or girl on the trail, then he spotted two. He probably improvised in his head. Maybe he zip tied their hands together so that one couldn't run off. Just the fact that it happened when there was no school, and a warm day in February, he probably had picked out the exact spot he would kill them, then casually walk off to his car close to the cemetery. I bet it was well thought out. Pure evil.
I remember reading on facebook about 9pm I believe that two girls were missing on the Monon trail in Delphi, I immediately wanted to jump in the car and go search. Then I read they were going to halt the search until the morning, but they knew the girls weren't dressed for the cold the night would bring. It hurt my heart, those poor girls.