Answer by taking a quote from the following article:

John Bruce "Jack" Thompson (born July 25, 1951) is an American activist and disbarred attorney, based in Coral Gables, Florida. Thompson is known for his role as an anti-video-game activist, particularly against violence and sex in video games. During his time as an attorney, Thompson focused his legal efforts against what he perceives as obscenity in modern culture. This included rap music, broadcasts by shock jock Howard Stern, the content of computer and video games and their alleged effects on children.

Thompson has heavily criticized a number of video games and campaigned against their producers and distributors. His basic argument is that violent video games have repeatedly been used by teenagers as "murder simulators" to rehearse violent plans. He has pointed to alleged connections between such games and a number of school massacres. According to Thompson, "In every school shooting, we find that kids who pull the trigger are video gamers." Also, he claims that scientific studies show teenagers process the game environment differently from adults, leading to increased violence and copycat behavior. According to Thompson, "If some wacked-out adult wants to spend his time playing Grand Theft Auto: Vice City, one has to wonder why he doesn't get a life, but when it comes to kids, it has a demonstrable impact on their behavior and the development of the frontal lobes of their brain." Thompson has described the proliferation of games by Sony, a Japanese company, as "Pearl Harbor 2". According to Thompson, "Many parents think that stores won't sell an M-rated game to someone under 17. We know that's not true, and, in fact, kids roughly 50 percent of that time, all the studies show, are able to walk into any store and get any game regardless of the rating, no questions asked."  Thompson has rejected arguments that such video games are protected by freedom of expression, saying, "Murder simulators are not constitutionally protected speech. They're not even speech. They're dangerous physical appliances that teach a kid how to kill efficiently and to love it," as well as simply calling video games "mental masturbation". In addition, he has attributed part of the impetus for violent games to the military, saying that it was looking "for a way to disconnect in the soldier's mind the physical act of pulling the trigger from the awful reality that a life may end". Thompson further claims that some of these games are based on military training and simulation technologies, such as those being developed at the Institute for Creative Technologies, which, he suggests, were created by the Department of Defense to help overcome soldiers' inhibition to kill. He also claims that the PlayStation 2's DualShock controller "gives you a pleasurable buzz back into your hands with each kill. This is operant conditioning, behavior modification right out of B. F. Skinner's laboratory."  Although his efforts dealing with video games have generally focused on juveniles, Thompson got involved in a case involving an adult on one occasion in 2004. This was an aggravated murder case against 29-year-old Charles McCoy, Jr., the defendant in a series of highway shootings the previous year around Columbus, Ohio. When McCoy was captured, a game console and a copy of The Getaway were in his motel room. Although not representing McCoy and over the objections of McCoy's lawyers, Thompson succeeded in getting the court to unseal a search warrant for McCoy's residence. This showed, among other things, the discovery of additional games State of Emergency, Max Payne, and Dead to Rights. However, he was not allowed to present the evidence to McCoy, whose defense team was relying on an insanity defense based on paranoid schizophrenia. In Thompson's estimation, McCoy was the "functional equivalent of a 15-year-old," and "the only thing insane about this case is the (insanity) defense".

Was Thompson able to show the games influenced the defendant?
he was not allowed to present the evidence to McCoy, whose defense team was relying on an insanity defense based on paranoid schizophrenia.