Police Wednesday tried to determine why a 19-year-old was killed after he lost control of his motorcycle on an east Visalia street and crashed into a tree.

Despite efforts by emergency medical technicians, Justin Minyard of Visalia was pronounced dead at the scene, Visalia police Sgt. Bill Blankenship said. The crash occurred about 2:30 p.m. on Ben Maddox Way north of Sunnyside Avenue.

Minyard was northbound on a Honda CVR600 motorcycle when he began to slow from a speed of about 40 mph, a motorist told police.

The witness reported changing lanes, passing the motorcycle and then seeing nothing in his rear-view mirror.

Minyard had been knocked from his motorcycle after hitting the tree, Blankenship said. The cause of the crash was unclear Wednesday afternoon.

Ben Maddox curves in the area, police said. The initial investigation indicated that the Honda hit the curb, rolled along it for 20-30 feet and jumped the curb, Blankenship said.

After hitting the tree, the motorcycle continued forward, hit another tree and rolled back onto the street, where it fell over.

Blankenship said the impact of the crash knocked Minyard''s helmet off even though it had been strapped on. The chin strap did not break, he said, but it was unclear whether it had been properly fitted.

"Some people wear their helmets too loose," Blankenship said, "and that''s not a good idea."

The speed limit along that stretch of Ben Maddox is 65 mph, and speed did not appear to be a factor, Blankenship said.