OAKLAND -- A conglomerate of mechanical issues, medical problems and police activity on BART caused systemwide delays Wednesday morning, officials said.

The morning's back ups began about 7:30 a.m. in the Fremont and Richmond directions after passengers reportedly jammed doors on some of those trains, BART spokeswoman Alicia Trost said.

The problem had a ripple effect through the system, delaying all lines except in the San Francisco International Airport and Dublin-Pleasanton directions.

Then at 8 a.m., the Pittsburg-Bay Point line backed up after a person suffered an unknown medical issue, Trost said.

Shortly after that, at 8:22 a.m., BART police stopped a train at the Coliseum station to search for a bike-theft suspect on a train there, Trost said.

The search caused a back up for trains behind that one.

It was not immediately known if police apprehended the suspect.

As of about 9:20 a.m. trains were moving, but still on a 15-20 minute delay.

"All of those things on their own wouldn't cause major delays but when they happen around the same time on the same lines it backs everything up," Trost said.

Contact Natalie Neysa Alund at 510-293-2469. Follow her at Twitter.com/nataliealund.