Reportedly, the incident took place at around 6:30 am, when Bachchan was out on a morning walk at the Globe Park in Hazratganj.
Bachchan's friend, Ashish Srivastava, who accompanied him on the morning stroll, was also injured.
Here are more details.
Bachchan shot in the head multiple times: Report
Bachchan, a resident of Gorakhpur, was on his morning stroll when bike-borne assailants reportedly opened fire at him.
Bachchan was shot in the head multiple times, India Today reported.
According to News18, he was shot at from a "close range" and was killed instantly.
A Hindustan Times report stated that Bachchan's friend was injured and admitted to the King George's Medical University (KGMU).
Six teams constituted to probe the case
Six investigation teams have reportedly been constituted to probe Bachchan's killing.
A police sub-inspector told HT that the assailants tried stealing Bachchan's gold chain and a cell phone before shooting him.
The officer, however, added that this could be a ploy to color the killing as a loot attempt instead of a "planned murder."
The police are now probing the case from "all angles."
Culprits will be behind the bars soon: DCP
Deputy Commissioner of Police (Central Lucknow) Dinesh Singh was quoted as saying by HT, "Forensic experts are scanning the spot. We have been scanning CCTVs and probing the case from all angles. The culprits will be behind the bars soon."
Bachchan's killing comes months after Kamlesh Tiwari's murder
This is the second killing of a Hindu outfit leader in Lucknow in the recent past.
In October last year, Hindu Samaj Party leader Kamlesh Tiwariwas killed at his Khurshid Bagh residence by two assailants.
An autopsy revealed that Tiwari was "stabbed at least 15 times and shot once."