The westbound train, which started its journey in San Bernardino and was heading to downtown Los Angeles, was between the Pomona and Covina stations when it struck the man about 4:30 p.m., said Los Angeles County sheriff's Lt. Lester Trull.
The man's identity is being withheld pending notification of next of kin. He was approximately 30 to 40 years old, according to Covina police Sgt. Ryan Davis.
Detectives with the Covina Police Department are investigating the death, Davis said. "It appears that it's a suicide at this point," he said, but investigators have not ruled out the possibility that the death was accidental.