OVERLAND PARK, Kan. — During Saturday's massacre inside Pittsburgh's Tree of Life synagogue , the shooter yelled out anti-semitic remarks.
"He walked in and said 'All Jews must die' and opened fire," Debi Salvin, one of the victims' twin sister told NBC News.
The rampage was a flashback to the 2014 deadly shooting in Overland Park outside of the Jewish Community Center and Village Shalom.
The convicted gunman, Frazier Glenn Cross, is a former Ku Klux Klan leader from Southern Missouri.
Cross became well-known to the Southern Poverty Law Center, which tracks hate groups across the U.S.
According to the center , the number of hate groups has grown from 784 in 2015 to 953 currently.
Since the 2014 shooting, there have been two instances where people in Overland Park have been targeted because of their religion.
"A lot of it has to do with the rhetoric, the vitriolic rhetoric—very propaganda—in our political environment, which seems to encourage violence," said Michael Tabman, a retired FBI special agent in charge.
Tabman believes radicalizing is easier now than ever.
"They only need to connect with one. One person who is on the edge. One person who has this predisposition of violent, anti-social behavior and they hear the message they want to hear. So it's telling them, 'It's ok, it's time,'" Tabman said.
While law enforcement can monitor chatter on social media platforms to try and prevent the next attack, Tabman said old-school investigative techniques are best.
"That we can recruit informants and people to tell us what's going on, what's being said behind closed doors. That is how we will stop the next violent attack," Tabman said.
Ultimately, a judge sentenced Cross to death for his crimes. The Pittsburgh suspect, Robert Bowers, faces the same fate if convicted.