PENDLETON — A wandering dog and a malfunctioning tractor-trailer reportedly caused a four vehicle crash that kept traffic along Interstate 69 moving at a slow pace for about seven hours Sunday.

The cause of the accident was likely a dog crossing the interstate, investigators said. At one point, the dog was reportedly struck by a vehicle. However, animal officers arriving at the scene near mile marker 20 could not find the dog.

The incident began at about 10:08 a.m. Sunday, when drivers saw the black medium-sized, mixed-breed dog running in the northbound lane near mile-marker 20 along I-69, said Master Trooper Alexander Willis of the Indiana State Police.

Cars began slowing dow to about 20 miles per hour, he said.

A 2009 International tractor-trailer, driven by Jeffery L. Taylor, 43, of Michigan, also slowed. A pin on the trailer came loose and the rear tires “dropped” from the trailer. The rear eight wheels and connecting axle of his tractor-trailer came loose and fell into traffic coming from behind him, Willis said.

The events resulted in a chain reaction crash, Willis said.

A beige 2007 GMC Envoy driven by Melissa N. Levi, 30, of Indianapolis, swerved to miss the axle and tires but her Envoy was struck from behind by a 2005 Freightliner tractor-trailer driven by Robert L. Jones, 47, of Michigan.

The Envoy was pushed into a 2007 Jeep Liberty driven by Pamela Marcoff, 54, of Indianapolis.

There were three passengers in Levi’s Envoy 54-year-old Deborah Levi of Indianapolis, who suffered a bruised forehead and back and hip pain; 17-year-old Jasmine Morst, who suffered back and neck pain, and 6-year-old Jaiden Marshall who was not injured.

Melissa Levi complained of neck and back pain.

Levi and her three passengers were treated and released from Saint John’s Medical Center in Anderson.

No other injuries were reported at the scene.

Indiana State Police Commercial Vehicle Enforcement Officers inspected Taylor’s trailer and found that a locking pin which holds the axle to the trailer was not engaged, according to Sgt. Mike Burns of the Indiana State Police.

Taylor was arrested at the scene for driving with a suspended license and ticketed for multiple equipment violations reportedly discovered during the inspection of the tractor-trailer.

The tractor-trailer had been carrying heavy rolls of paper that were off-loaded at the scene before the lanes could reopen, Burns said.