Police are investigating a shooting on a CTA Pink Line train in The Loop early Tuesday morning. 

Video from the scene showed Chicago police canvassing the area around Wells and Randolph streets around 1:30 a.m. Police were investigating inside a train car with evidence markers next to shell casings. 

The circumstances surrounding the shooting have not been released. 

CTA officials confirmed Pink, Green, Orange and Brown Line trains are running with residual delays. 

On Friday, the CTA submitted a safety plan in response to threats made by the Trump administration to withhold funding should the CTA not improve safety. However, the Federal Transit Administration said that won't be enough, and is giving the CTA 90 days to respond with a better safety plan.

The FTA cited last month's attack on a 26-year-old woman, who was set on fire on a Blue Line train in downtown Chicago, in making their demands.  

This is a developing story. CBS News Chicago will continue to provide updates.