"Connection with the attack" refers to the involvement or relationship someone has to a specific incident or act of aggression. It implies that the person has some kind of link or association with the attack. Full definition
A man sentenced to 107 years in prison in connection with an attack on his former girlfriend, her friend and her father could be facing additional prison time. (news.wbfo.org)
The report said further that the number of people held in connection with the attack now stands at 43, including the wife of the suspected attacker. (nigeriapoliticsonline.com)
It's not clear what prompted the shooting, but police are questioning three men in connection with the attack. (articles.chicagotribune.com)