In reality it could have been back tracked, to the start if the bridge, further back, then cctv along the streets.
It's just man power and willingness to do it
"In reality" you're underestimating how time-consuming it is to retrieve footage and then trawl through said footage. It's not like the movies where the police can just tap in to all the CCTV in all the country and find what they're looking for in 30 seconds. There's a reason the CCTV images were only released to the public weeks after that bridge incident, and it isn't because the investigating officer(s) was sitting on their arse waiting for the case to solve itself.
In the case of a serious incident or a terrorist attack things can obviously be made to move along more quickly, but there's no immediate rush for someone pushed over on the street.