"From there phone data records state Cantrell and Dudley’s phones were at his Tacoma home. About an hour and a half after she appeared to arrive, according to phone records, Dudley places a call to his home security company, ADT. Detectives note shortly after, he texted his wife the power was also temporarily out and said "don’t freak out if the ADT cams are down."
An hour later, Dudley’s phone shuts off, but Cantrell's doesn’t. The data shows it leaves Dudley’s home and travels to the train station where at the same time her car is dropped off. And when Dudley’s truck is captured leaving the train station not long after, records show her phone traveled with it. The phone's final destination point recorded was at 12:45 p.m. in an area similar with Owen Beach, where divers would later find it buried in sea kelp on the ocean floor.
About 45 minutes after investigators believe Cantrell's phone was thrown in Puget Sound, Dudley’s phone turns back on and places him at his residence. He texts his wife at 2:30 p.m. seemingly about the security cameras being back on, and just prior, texting his employer asking about sealant, a substance used for sealing and filling gaps and cracks. Dudley mentions to his boss he’s doing work in his basement. One week later, FBI forensic technicians would search his home, detecting blood in various areas of the basement and also in his truck."
Kassanndra Cantrell: Body of missing pregnant woman found in Pierce County; suspect arrested
Lots of details in the above link. I'm still unsure which vehicle he used to transport her body to University Place but it seems it would be her car as his truck is parked at the public garage. Also, he took precautions to inactivate his home security system, but forgot to turn off her phone. Seems it was that error that told LE the entire story.