The accused, who is now in custody, had said that he opened fire to avenge the murder of Chandan Gupta.
The youth's now deleted Facebook post also had several mentions of 'Chandan bhaiyya'.
Chandan's mother, Sangeeta Gupta, meanwhile, has condemned the firing incident at Jamia.
"I condemn the act of opening fire at the Jamia protesters in the strongest possible words. We are a non-violent society and protest should always be peaceful. I have lost my son to one such act of violence," she told local reporters.
Gupta further said that she had lost her son to violence and even he did not approve of violence.
"I do not approve or appreciate violence in any form," she said.
Sources said that the accused in Jamia firing wanted to whip up a frenzy that would help him avenge Chandan's death.
Another family member, who requested anonymity, said: "The Jamia incident was wrong. There should be no support for the accused because this will encourage others to follow the same path."
Chandan Gupta and his friends were taking out a 'Tiranga Rally' in Kasganj on the Republic Day in 2018 and a dispute emerged over clearing the road for the rally. This led to violence and the 22-year-old was shot dead, after which communal riots broke out in Kasganj.
( With inputs from IANS )