TULSA, Oklahoma - A mother and father are left with more questions than answers after their son died in a motorcycle accident nearly one month ago.

Derek and Mona Tyner tell News On 6 and our partner, The Frontier, not all witness accounts of their son’s death are matching police reports.

The Tyners lost their 18-year-old son Cobie on Mother's Day. They said they haven't been able to grieve as they wait to learn exactly what happened.

"I go there every day and look at that accident and try to figure it out," Derek Tyner said.

Cobie died on May 14th, 2017, when his motorcycle ran into oncoming traffic near Chandler Park.

Riding was Cobie's passion, and he was riding with about 20 people around a curve when the wreck happened.

"There was a group behind him and a group in front of him," Tyner said.

He said those witnesses say Cobie had no options.

"He came around that corner and he had nowhere to go because there was a Tahoe in the road," Tyner said.

The initial Oklahoma Highway Patrol report says Cobie "…crossed the center line for an unknown reason."

But, according to the Tulsa County Sheriff's Office report, there was a reason.

"There was an officer in the road," said Tyner.

The sheriff's office report says Deputy Andrew Titsworth was "…traveling west on Avery Drive…" and saw a motorcycle speeding. In the report, the deputy says "traffic was clear so he pulled to the shoulder and conducted an uninterrupted turnaround."

That's when the deputy says he looked out the window and saw a motorcycle hit a white sedan.

The deputy says he checked on the rider and tried to help, but Cobie's dad said witnesses have a different story.

"He wouldn't even help him. He wouldn't even check on him," Tyner said.

Other riders tell him they came back but were told to leave.

Tyner said, "He told them 'they all had to leave.”

But, the sheriff's office report says the deputy asked them "…to remain on scene and talk to OHP…" but none did.

Cobie’s parents are left trying to piece together the facts and understand why stories don't seem to match.

"I can't get an accident report and it's going on four weeks," Tyner said.

OHP is still investigating. They are waiting on toxicology and Medical Examiner reports, and still need to speak with more witnesses.