I’m reading Dr Waḻa’s testimony (per trial transcript and being questioned by Ms. Diener for the State). I’m reading a copy posted by Tom Webster, link here
Tom Webster - Delphi trial transcripts vol 17 starting page 72. Based on this, I think it’s possible he did see the van from the other side of the creek (having already crossed over).
Q What did he tell you?
A So he said he wanted to confess to his crimes and went on to tell his story.
He reported seeing his parents the morning of the crime. He stated he was
supposed to go eat with them, but opted to get himself a six-pack. He reported
drinking three beers and then finishing the rest later. He stated, “I bundled up.”
Once on the trail, he stated, “I laid in wait.” He reported seeing the girls and
following them to the bridge. He mentioned doing something with his gun and
stated, “I think that’s where the bullet fell out.” And then he said, “I ordered
them down the hill.” He stated his intention was to rape the girls and mentioned
he thought they were older than their biological ages. He said he saw a van,
which scared him and caused him not to follow through on raping the girls. He
said they crossed a creek and then he cut their necks. He indicated wanting to
make sure they were dead. He reported covering their bodies with tree branches.
He said he exited the area by keeping off the trail as to not be seen. He said he
returned to his vehicle, which he parked by a nearby building. He stated he
managed to continue living his life after time passed by and he hadn’t been
caught.