SPRINGFIELD, MASS. >> A man riding what police say was a stolen motorcycle has died in a crash in Springfield.

Police say the operator was seriously injured when he was thrown from the 2005 Yamaha after it jumped a curb and struck a stop sign at about 6 p.m. Sunday.

The operator, identified as 26-year-old Jonaid Martinez, was taken to Baystate Medical Center where he was pronounced dead.

Investigators think speed was factor in the crash. The motorcycle had been reported stolen in Chicopee.

The accident remains under investigation.